List of characters in mythology novels by Rick Riordan
This is a list of characters that appear in the Camp Half-Blood chronicles (which consists of the Percy Jackson & the Olympians series, The Heroes of Olympus series, and The Trials of Apollo series), The Kane Chronicles, and Magnus Chase and the Gods of Asgard.
- 1 Camp Half-Blood Chronicles
- 1.1 Percy Jackson and the Olympians main characters
- 1.2 The Heroes of Olympus main characters
- 1.3 The Trials of Apollo main characters
- 1.4 Greco-Roman deities
- 1.5 Demigods
- 1.6 Mythological figures
- 1.7 Other Greco-Roman beings
- 2 The Kane Chronicles
- 3 Magnus Chase and the Gods of Asgard
- 4 Mortals
- 5 References
Camp Half-Blood Chronicles
Percy Jackson and the Olympians main characters
Perseus "Percy" Jackson is a demigod son of the mortal Sally Jackson and the Greek god Poseidon. He is the main protagonist and first-person narrator in the Percy Jackson & the Olympians series and appears in every book of the Camp Half-Blood chronicles except The Lost Hero. In his most recent appearance in The Hidden Oracle, the seventeen-year-old Percy states that he and his girlfriend Annabeth Chase plan to finish senior year in New York before heading to the college in New Rome.
Percy is described as having a "Mediterranean" complexion, with black hair and his father's sea green eyes. The powers he inherited from his father include controlling water, making hurricanes, breathing underwater, and talking to horse-like animals and sea creatures. He is also a notably good swordsman. Throughout the series, Percy fights by using a ballpoint pen named Anaklusmos (Ancient Greek for "riptide") that changes into a "celestial bronze" sword. Percy's fatal flaw is excessive personal loyalty, which he does not at first see as a danger.
In the films, he is portrayed by Logan Lerman.
Annabeth Chase is one of protagonist Percy Jackson's closest friends and later his girlfriend, first appearing as a twelve–year-old who helps nurse him back to health after he fights the Minotaur. She is the daughter of the goddess Athena and mortal history professor Frederick Chase, from whom she has an extensive paternal family. Annabeth has blond hair, stormy gray eyes, and tan skin. As a daughter of Athena, she is naturally intelligent, with a particular gift for strategy and architecture. At the end of The Last Olympian, she is even assigned to redesign the damaged Mount Olympus. Her fatal flaw is hubris, which is excessive pride. She is also described by her teacher Chiron as "territorial about her friends", which is manifested in several moments of jealousy and distrust. In The Lightning Thief, it is revealed that she is terrified of spiders.
Annabeth runs away from her father and stepfamily at age seven and encounters Luke Castellan and Thalia Grace. They live as runaways until they are found by Grover Underwood and taken to camp. Annabeth remains attached to Luke and convinced of his goodness even after his decision to support Kronos. Her attempts to bring Luke back into the fold are an important theme in the books. Annabeth is crucial to the plot of each book in the Camp Half-Blood Chronicles, in various ways. She leads quests in The Battle of the Labyrinth and The Mark of Athena. She also spends some time in Tartarus with Percy and Bob the Titan during the House of Hades. At the end of the series, she and Percy plan to finish high school in New York and then attend college in New Rome. In The Hidden Oracle, Percy states that Annabeth had gone to Boston for "some family emergency"—searching for her cousin Magnus Chase. Annabeth's appearances in crossover shorts with The Kane Chronicles, and in Magnus Chase and the Gods of Asgard make her the only character who has appeared in all three of the Greco-Roman, Egyptian, and Norse mythology series by author Rick Riordan.
Her main weapon is a short celestial bronze knife given to her by Luke. After losing it in The Mark of Athena, she uses a drakon-bone sword given to her by the giant Damasen. She also uses Sadie Kane's wand when it turned into a dagger like the one Luke gave her. Annabeth also uses an invisibility Yankees cap from her mother and a magic shield. At the end of The Battle of the Labyrinth, Daedalus gives Annabeth his incredibly advanced laptop computer which she loses on the depths of Tartarus.
In the film adaptations, she is portrayed by Alexandra Daddario.
Grover Underwood is a satyr who is Percy's best friend. In the books, he has curly brown hair and fur, acne, a wispy beard. His horns grow larger as the series progresses, and he must take increasingly careful measures to hide them and his goat legs while posing as human. He is a vegetarian but also eats tin cans, furniture, and enchiladas. Grover is twenty-eight in the first novel, but because a satyr's lifespan is twice that of a human, he is still physically a teenager. Grover is a very sensitive and nature-conscious person. Like all satyrs, he can sense emotions and "smell" monsters and demigods. As the series progresses, his concern for his friends and pursuit of his goals lead him to take on leadership roles and become more sure of himself. Unlike his demigod friends, Grover is not an orthodox fighter. Instead, he uses reed pipes or a cudgel.  In The Battle of the Labyrinth, Grover begins a relationship with the dryad Juniper.
He is first seen in The Lightning Thief, where he is disguised as a human student at Percy's school, serving as his "protector". Grover later reveals that if he completes a protector mission, he will receive his "searcher's license", and leave to look for the missing god Pan, his life's ambition. When Polyphemus captures him in The Sea of Monsters, he forms a psychic bond with Percy, called an empathy link, allowing them a limited degree of telepathic communication across great distances. He uses this ability to guide Percy to his rescue. He eventually finds Pan in The Battle of the Labyrinth, and receives the wild god's spirit. At the end of The Last Olympian, he is named a Lord of the Wild and given a seat on the satyrs' ruling council.
In the film adaptations, Grover is portrayed by Brandon T. Jackson.
Luke Castellan is a 19-year-old demigod (in The Lightning Thief), the son of Hermes and May Castellan. Introduced as the friendly head counselor of the Hermes cabin, he is soon revealed to be a servant of Kronos. Luke is resentful of his father, who adhered to the gods' policy of non-interference despite May Castellan's mental illness. Luke runs away from home young and eventually arrives at Camp Half Blood. After the loss of Thalia, a failed quest, and continued silence from his father; his ongoing resentment turns into a strong hatred of not only Hermes, but all the gods. Though described by those who knew him before he joined with Kronos as a nice guy, he later becomes moody and violent.
Luke is described as handsome with sandy hair, blue eyes, and a long scar on his cheek given to him by Ladon. He is first and foremost an excellent swordsman. He even receives a sword named "Backbiter" from his master Kronos at the end of The Lightning Thief. This sword, which is later reforged as Kronos's scythe, has the ability to harm both mortals and monsters. From the demigod Halcyon Green, he receives a celestial bronze knife and diary. Luke later gives this knife to Annabeth with a promise to always remain her family and entrusts the diary to Chiron. From his father he receives a pair of magic flying shoes, which he later curses and gives to Percy. He has also inherited an ability to open locks with his mind, along with a cunning nature, from his father. Just before giving himself over completely to host the spirit of Kronos, Luke bathes in the River Styx and obtains the invincibility of Achilles.
Though Luke originally serves Kronos willingly, the horrors he witnesses during the Battle of Manhattan convince him to fight against his former master, eventually committing suicide to stop the Titan. By doing this, Luke proves himself to be the "hero" of the Great Prophecy. As he dies, Luke reiterates what Ethan Nakamura tells Percy earlier: that unclaimed children and unrecognized gods deserve more respect than they have been given.
In the films he is portrayed by Jake Abel. In this version, Luke is also incredibly skilled in unarmed combat, easily overpowering Percy when the latter was carrying the sword.
Thalia Grace is the daughter of Zeus and Beryl Grace, a TV starlet the god met in the 1980s. In The Lost Hero she is revealed to be the older sister of Jason Grace. Due to her mother's abusive nature, Thalia has considered leaving home since she was little, but stays to protect Jason from her mother's antics. However, when Jason is apparently killed during a visit to Sonoma (in actuality, he is merely presented to Hera), Thalia finally runs away at age 9 and stays with Luke and Annabeth until they meet Grover Underwood when she is 12. When the party reaches Camp Half-Blood, Thalia gives her life to hold off pursuing monsters on top of what would later be called Half-Blood Hill. To save Thalia's life, her father transforms her into a pine tree. Her spirit then provides a magical barrier that protects the camp until six years later when it is purged from the pine tree by the Golden Fleece.
Thalia is pursued so fiercely by monsters because she is a violation of the "Big Three Oath", which was a promise between the three eldest male Olympians to have no more children, for fear of "The Great Prophecy" coming true. At the end of The Titan's Curse, she joins the Hunters of Artemis, a band of immortal female archers in service to the goddess Artemis. This freezes her age the night before her sixteenth birthday, taking her out of the running for the prophecy.
Thalia has electric-blue eyes and spiky black hair, and wears dark makeup and punk style clothing. Annabeth remarks that Thalia's personality and character traits—such as her bravery and loyalty—are very similar to Percy's, and the centaur Chiron later says much the same. She also shares some traits with her father Zeus, including sometimes over-the-top pride, confidence, and reactions to betrayal or contradiction. She is also an incredibly skilled warrior, willing to attack even Luke, recognized as the best swordsman Camp Half-Blood has ever known. Thalia's weapons of choice are at first a shield named Aegis disguised as a silver charm bracelet (this gift from her father causes paralyzing fear in those who see it because the head of Medusa is pictured on the shield), and a spear disguised as a Mace canister. After The Titan's Curse, she uses a bow and hunting knives, but still uses Aegis. Her main "power" is the ability to summon lightning and generate electric shocks. In The Titan's Curse, it is revealed that she has a fear of heights. In The Lost Hero, she makes a minor appearance and embraces her brother Jason for the first time in years, only to learn that he had lost his memory.
In the film Percy Jackson: Sea of Monsters, she is portrayed by Canadian actress Paloma Kwiatkowski. It was shown that the Cyclopes were the ones who attacked her, Annabeth, and Luke outside of Camp Half-Blood.
Tyson is Percy's younger brother. In The Sea of Monsters, he is introduced as Percy's bullied, childish friend. When Percy is forced to take him to Camp Half Blood, it is revealed that he is a baby Cyclops and a son of Poseidon making him Percy's half-brother. Percy is at first resentful of him as a brother, while Annabeth is openly hostile towards him, but both accept him after they get to know him better during a quest to the Sea of Monsters.
Tyson is described as tall with unkempt teeth and fingernails, and brown hair and eye. He is mentally about 8 years old, but fairly intelligent and extremely compassionate. As a son of Poseidon, Tyson has some limited powers over sea creatures and water. As a Cyclops, he is immune to fire and super-strong; has an uncanny ability to mimic voices; has enhanced senses; and can understand the "old tongue" (the language spoken by Gaea to her first children). Tyson also becomes an excellent smith with help from Beckendorf. In The Last Olympian, he proves himself also to be a capable fighter and is named a general of Poseidon's armies. He leads his fellow Cyclopes into the fight with battle cry of "Peanut Butter!"
Tyson is close with several characters and magical creatures in the series. The first is Rainbow the hippocampus. He also befriends the hellhound Mrs. O'Leary. In The Battle of the Labyrinth, Tyson is revealed to be afraid of satyrs, including Percy's friend Grover; he manages to conquer this fear after a quest with Grover, and befriends the satyr. In the Heroes of Olympus series, Tyson also begins a romantic relationship with the harpy Ella.
In the Percy Jackson: Sea of Monsters movie, he is portrayed by Douglas Smith.
Nico di Angelo
Nico di Angelo is first seen in The Titan's Curse, as an unclaimed demigod rescued by Percy, Annabeth, Thalia, and Grover. At the end of the novel, it is revealed that Nico is a son of Hades. Though he appears to be ten years old and therefore a violation of the "Big Three Oath", in reality he and his elder sister Bianca were born sometime in the 1930s, before Hades took the oath; and, after having their memories wiped in the Lethe, stayed in the Lotus Hotel and Casino until the present day. Their mother was Maria di Angelo, daughter of an Italian diplomat. He is a native of Venice, Italy and can speak Italian.
Nico is initially depicted as cheerful and childish, with olive skin and dark hair, and enjoys playing Mythomagic (a Greek-mythology-themed card game similar to Magic: The Gathering). After Nico learns of Bianca's death, he becomes moody and secretive. Afterwards, he becomes pale and shaggy-haired and begins wearing dark clothing. Nico, despite being very powerful, is extremely lonely, much like his father. He makes many other characters uncomfortable, in part due to his powers over darkness and death and his unnerving weapon of choice: a sword made of iron cooled in the Styx ("Stygian iron") capable of absorbing monsters' essences, rather than simply banishing them to Tartarus. Nico initially blames Percy for Bianca's death, but forgives him after learning that holding grudges is likely his fatal flaw. From this point on until meeting Cupid in The House of Hades, Nico struggles to hide his homosexuality, something he was raised to believe was completely inappropriate. During 'The Blood of Olympus', Nico's task was to transport the Athena Parthenos to Camp Half-Blood along with Reyna and Coach Hedge, to bring peace between the Camp Half-Blood and Camp Jupiter. Sometime after the end of The Blood of Olympus, he begins a relationship with Will Solace.
Nico's suggestion that Percy take on the curse of Achilles and his work to convince Hades to fight in The Last Olympian are crucial to the Olympians' success, and earn him a short bout of fame. He was also privy to the fact that there were two camps, one Greek and one Roman, before The Lost Hero, which makes him an important liaison between the two groups in the latter series. He brings Hazel Levesque, daughter of Pluto and his half-sister, back from the dead and established her at Camp Jupiter. Between The Son of Neptune and The Mark of Athena, Nico travels through Tartarus to find the monstrous side of the Doors of Death, an experience which leaves him haunted and weak. In The Blood of Olympus, he nearly dies several times while "shadow-traveling", which involves melting into shadows and transporting himself to different places.
The character Nico was named after one of Riordan's former students.
Rachel Elizabeth Dare
Rachel is a main character in the later books of the Percy Jackson series and a minor character in the Heroes of Olympus series. Rachel is a mortal girl who can see through the Mist, the force that obscures gods and monsters from most mortals. She first meets Percy in The Titan's Curse at the Hoover Dam. In The Battle of the Labyrinth, she helps Annabeth and Percy by guiding them through the Labyrinth to Daedalus's workshop. It is hinted throughout the series that she harbors some romantic feelings for Percy; Annabeth notices this and becomes jealous. In The Last Olympian, she begins having strange visions and becomes the new Oracle of Delphi. Her first act as the Oracle is to deliver the next Great Prophecy about seven heroes, setting the plot of the Heroes of Olympus series. Her appearances in the sequel series is sparse; she is contacted by Annabeth in The House of Hades to ask for Reyna's assistance to bring the Athena Parthenos back to Camp Half-Blood.
Following the loss of Delphi to Python, as revealed in The Hidden Oracle, Rachel stops visiting Camp Half-Blood and begins in a frenzied attempt to regain her foresight, not helped by the disappearance of Apollo. Once informed of Apollo's arrival at Camp Half-Blood, Rachel returns and learns that not only Delphi is lost, so do three other Oracles, except for Dodona, which is owned by Rhea. She becomes upset upon learning of the existence of other Oracles, as Apollo has not told her before.
She is described as having red hair and freckles. She is skilled at painting and drawing, with both feet and hands, and is occasionally shown as a non-ADHD foil for her demigod teammates. Percy remarks on her ability to stand still for long periods of time at a charity event. Due to her limited power of foresight, Rachel knows a great deal of knowledge before she learns it herself; during her meeting with Reyna, she states the latter's full name, something that only Reyna's inner circle of friends know.
Clarisse La Rue
A daughter of Ares and the lead counselor of the Ares cabin at Camp Half-Blood, Clarisse is hot-tempered, courageous, and strong. As the child of a war god, she is an excellent fighter (usually utilizing an electric spear given to her by Ares) and a good military strategist. She can be stubborn and overconfident, much like her father, but often surprises other characters with her loyalty and leadership skills. Despite their similarities, Clarisse has a fear of her father and his anger at her if she should ever disappoint him—this, along with a strong sense of honor and pride, often motivates her actions. She also fears the Labyrinth because of what happened to the demigod Chris Rodriguez when he was inside the huge maze. She is aggressive towards most demigods, including Percy , though she does respect and make friends with a few: Percy, Annabeth and Silena Beauregard included. She eventually starts dating Chris.
Clarisse makes frequent appearances throughout the novels, first seen just after Percy arrives at Camp Half-Blood. In The Sea of Monsters, Clarisse is instrumental in bringing the Golden Fleece to camp. She is a main character in the short story "Percy Jackson and the Stolen Chariot" (published in Percy Jackson & the Olympians: The Demigod Files). In The Last Olympian, Clarisse initially sits out the war for Olympus due to a personal feud (like Achilles in the Trojan War).
Enraged after the loss of her friend Silena, she later joins the battle with a fury reminiscent of her father's, slaying a drakon singlehandedly and receiving the blessing of Ares. In The Blood of Olympus, Clarisse leads the Greeks in battle to defend the camp.
In The Hidden Oracle, it is stated that Clarisse has gone to attend the University of Arizona.
In the film adaptation, Clarisse is portrayed by Leven Rambin.
The Heroes of Olympus main characters
Leo Valdez is a 15-year-old demigod son of Hephaestus and the one of seven protagonists of The Heroes of Olympus. Leo is described as looking like a "Latino Santa's elf" with curly hair, brown eyes, a cheerful face, a slim build, and a mischievous smile. He is Hispanic-American and a native of Texas. He speaks Spanish. Leo has the ability to create and manipulate fire, a skill that no son of Hephaestus has had in 400 years. Leo is also an excellent mechanic. He repairs a bronze dragon running wild in the camp's woods, renaming it Festus. He also creates the Argo II, a ship the Seven sail on to reach Greece.
When he was eight, he was tricked into setting fire to his mother Esperanza's machine shop while facing off against Gaea, which resulted in Esperanza's death. Leo's remaining family blamed him for killing his only parent and left him a foster child and runaway. Leo also uses his sarcasm and wit to hide his feelings, especially in regards to having been the cause of his mother's death. He has a tendency to think of himself as a "seventh wheel", though he proves no less important or skilled than the others. In The Mark of Athena, Hazel learns her former boyfriend, Sammy, was Leo's great-grandfather. Until he falls in love with Calypso in The House of Hades, Leo falls quickly for almost any attractive girl he meets.
In The Blood of Olympus, Leo sacrifices himself to annihilate Gaea, and dies in the process. He is brought back to life using the "Physician's Cure" and returns for Calypso on her island of Ogygia. Following his resurrection, Leo goes on a journey with Calypso. As Leo is included in the prophecy of the Grove of Dodona, he accepts the task to accompany Apollo on his trials in The Trials of Apollo, together with Calypso.
Piper McLean is a daughter of Aphrodite and the famous actor Tristan McLean. She is fifteen in The Lost Hero. Unlike most children of Aphrodite, Piper is not particularly concerned with beauty or fashion. Piper is Cherokee on her father's side. She has tan skin, eyes that change color constantly, and choppy caramel/chocolate-colored hair which she cuts herself. She is slim build and of average height. Her demigod "powers" include "charmspeak" (essentially, magical persuasion) and the ability to speak French. She is also occasionally able to see visions in her magic dagger Katoptris (meaning looking glass in Ancient Greek), which once belonged to Helen of Troy. It is unclear whether this is due to the knife's magic or her own.
Piper's relationship with her father is mutually affectionate but strained, in part because of the small amount of attention he spares for her. When she was young, Piper used her persuasive skills to "borrow" things (such as a car, lawn mower, etc.) just to earn a little of his time. After he is kidnapped by the giant Enceladus in The Lost Hero and subsequently rescued by Piper, Jason and Leo; Mr. McLean's relationship with his daughter begins to improve. Piper is also very close to Jason. Though she later learns it was all a trick of the Mist, she was once his girlfriend while they attended the same school. She works hard to recreate this relationship in real life when she comes to Camp Half-Blood. She is also friends with all of the seven quest members in The Heroes of Olympus, especially Annabeth.
Piper's main weapon is her dagger Katoptris, though she later acquires a magic cornucopia and uses it as a weapon. After being captured by pirates in The House of Hades, Piper asks Hazel to teach her sword fighting, using a jagged celestial bronze sword taken from one of the Boreads.
In The Hidden Oracle, Nico mentions that Piper is currently attending school in Los Angeles, together with Jason.
Jason Grace is a son of Jupiter and the mortal Beryl Grace, a TV star of the 1980s, and the younger brother of Thalia Grace. Jason has few memories of his mother, who was compelled to give him up when he was two, but he remembers enough about Thalia to not be surprised when he sees her again, in The Lost Hero. Thalia reveals that their mother told her that Jason was dead, and that this was what finally drove her to leave home, after she run away from home and found "Camp Half-Blood . He later discovers, in The Blood of Olympus, that Beryl Grace had become a mania, or spirit of madness. He grew up at Camp Jupiter, the Roman equivalent of Camp Half-Blood, where demigods born to the Olympians' Roman aspects receive their training. In The Lost Hero, he begins a romantic relationship with Piper McLean.
Jason is described as having blond hair, blue eyes, and a scar above his upper lip (according to Thalia, this is the result of an attempt to eat a stapler when he was two). He is of above-average height, with an athletic build and muscular arms. He has a tattoo burned under his forearm, with twelve straight lines like a bar code, an eagle, and the letters SPQR over the lines. The tattoo symbolizes his twelve years of service in the Twelfth Legion Fulminata at Camp Jupiter; the eagle is a symbol of Jupiter. By the age of fifteen, he had earned the rank of praetor and led the legion with his longtime quest partner, Reyna. Jason also coordinated the Roman camp's attack on the Titan force. He led an assault against Mount Othrys, a Titan stronghold near San Francisco, and defeated the Titan Krios in combat, much as Percy Jackson defeated Kronos.
Of all the characters in the series, Jason is the one who struggles the most with the differences between the Greek and Roman perspectives. Piper McLean describes Jason as very rule- and duty-oriented, though the Roman god Terminus describes him as a "rule-flouter." However, when his former compatriot Reyna sees him again in The Mark of Athena, she comments that he seems to have lost some of his Roman qualities. When the Argo II is stuck in North Africa, he realizes that he must choose one identity or the other. He chooses to consider himself a Greek, despite his parentage, and is later unable to command a legion of ghosts sworn to obey only Roman officers. During The House of Hades it is revealed that Jason has plans to return to Camp Jupiter to improve it with things he learned at Camp Half-Blood, such as giving the fauns (the Roman equivalent of a satyr) more rights and responsibilities. Later, during The Blood of Olympus, Jason decides to consider both the Greek and Roman traditions as part of his heritage. He becomes "Pontifex Maximus", a role which will see him travel between Camp Half-Blood and Camp Jupiter to build shrines for every god and goddess in the pantheon, allowing him to stay in touch with both sides.
Although Jason and Percy immediately recognize that it is best to work together, and become friends, their relationship is not without antagonism. As Percy puts it, it is natural for two powerful demigods to wonder which of them is stronger after a fight. Jason is a sword fighter like Percy, though they have different fighting styles. Jason uses an Imperial gold sword, styled as a Roman gladius, which he can extend into a pilum at will. It is possible that this is a trait common to all Roman demigods, as Reyna is also shown as able to turn her sword into a pilum. Jason also has power over air currents and can fly. He can sense and control some air spirits and has, like Thalia, called down lightning, which he conducts through his Imperial Gold weapons, even underwater. On one occasion, he and Percy together summon a hurricane in Charleston harbor. Like his sister, Jason can also emit static shocks, which seem to be tied to his emotions.
The Hidden Oracle reveals that Jason has been attending school in Los Angeles with Piper, as per Nico's words.
Hazel Levesque is a thirteen-year-old demigod, a daughter of Pluto and Marie Levesque. She first appears in The Son of Neptune, at Camp Jupiter. It is later revealed that she has returned from the dead, assisted by her half-brother Nico. She grew up in the 1940s in New Orleans, where her mother had a gris-gris shop. When she was born, Pluto offered to grant her mother a wish, but her request for wealth backfired into an ability to control precious metals and gems, which both first view as a curse. Hazel died after Gaea tries to use Hazel's power over earth to resurrect Alcyoneus. When Hazel's mother changes her mind about helping Gaea, Hazel buries herself and her mother under the earth, delaying Alcyoneus's rebirth and killing them both. While Hazel's spirit is being judged, she gives up the chance to go to Elysium to save her mother from punishment, and they are both sent to the Fields of Asphodel instead. At some point before The Lost Hero, Nico finds Hazel in the Underworld while investigating an imbalance between life and death. He helps her escape to the world of the living and arranges for her to join Camp Jupiter. Hazel and Nico are protective of each other, much as true half-siblings.
Hazel is described as African American, having cocoa-colored skin, curly cinnamon-brown hair, and golden eyes. Her legion tattoo is described as looking like a cross with curved arms and a head. She eventually learns to manipulate her curse, manipulating precious stones and metals and sensing structures underground. She is an accomplished horse-rider and skilled with a spatha. She tames the horse Arion, who eats precious metals. She is unusually knowledgeable about the Underworld because of her time there. During The House of Hades the goddess Hecate insists Hazel learn to manipulate the Mist. Hazel becomes very gifted at this. After the Second Gigantomachy, Hazel is promoted to the rank of centurion of the Fifth Cohort, succeeding her boyfriend Frank.
Frank Zhang is a 16-year-old demigod, son of Mars and a Chinese-Canadian "legacy" (descendant of a demigod) who dies during military service in Afghanistan. He is taken care of by his grandmother after his mother's death, and makes his way to Camp Jupiter upon her insistence. Frank's family descends from Periclymenus, a grandson of Poseidon, who had the power to shapeshift. Periclymenus's descendants were sold into slavery in China, and migrated to Canada many years later. While battling Alcyoneus (who is invincible within Alaska), Frank taps into his ancestral power and transforms into an elephant. However, his combined power of being a son of Mars and having the ability to shapeshift makes his life very fragile. The Fates tied his life force to a piece of firewood when he was a baby....if the wood burns up, he will die (as in the ancient Greek legend of Meleager). The goddess Juno appears to his mother and grandmother while he is a baby to warn them of this fact, as he would be crucial to defeating the Giants. In all his life, Frank has ignited the wood twice, which he can do simply by thinking about it; the first time is while he is finding his way to Camp Jupiter, in bitter cold. The second time is when he, Percy, and Hazel travel to Alaska to free Thanatos. Eventually, Frank entrusts the firewood to Hazel, and in The House of Hades, Leo creates a fireproof pouch to contain it.
Frank has a meek disposition and is uncomfortable upon learning his father's identity publicly in front of the whole of Camp Jupiter. He suspected himself a son of Apollo, given his skill with a bow and arrow. On his quest in The Son of Neptune, and later during the series as well, he uses an enchanted spear given to him by Mars. To Frank's surprise, the spear summons a skeleton warrior that defeats the basilisks. Frank calls this skeleton "Gray".
As he has been residing in Camp Jupiter for no more than a year, Frank is initially considered a probatio, or rookie, of the Fifth Cohort. Before the quest to free Thanatos, however, his cohort's centurion, Gwen, decides to retire and give her position to Frank. Later, in The House of Hades, Jason surrenders his praetorship to Frank, who uses its authority and the Diocletian's Scepter to lead an army of Roman skeleton soldiers against the monsters in the Necromanteion.
Frank was described as 'cuddly' and 'fuzzy' and with a chubby, babyish face in The Mark of Athena, but in The House of Hades, after summoning the blessing of Ares to defeat a hoard of enemies, he transforms. He is then described as being taller, more muscular, and without all his childhood fat. Though now built like a professional football player, he is still as sensitive as before, and is embarrassed at his new appearance at first.
Initially, he was wary of the tension between Hazel and Leo, as Leo reminded Hazel of her old boyfriend, Sammy Valdez. After Leo's encounter with Calypso, however, Leo became more relaxed around Hazel and there were no more signs of anything other than friendship, much to Frank's relief. He then pursues a relationship with Hazel.
Reyna Avila Ramírez-Arellano
Reyna Avila Ramírez-Arellano is a 16-year-old Puerto Rican demigod. She is a daughter of Bellona, a Roman Goddess, and the younger sister of Queen Hylla of the Amazons. She and her sister worked for Circe during the events of The Sea of Monsters. She is described as intimidating and a natural leader; she has glossy black hair and black eyes. Reyna is generally more used to responsibility than other demigods, as she is a praetor at Camp Jupiter. Reyna's demigod "power" is the ability to lend her energy, skills, and character traits to nearby demigods. Like Leo Valdez, she can speak both English and Spanish. Reyna is often accompanied by two magical dogs, Aurum and Argentum, or by her pegasus Scipio ("Skippy" dies at the end of The House of Hades). The immortal winged horse named Pegasus awards her the title of "Horse Friend", because of her kindness towards Scipio and other of his descendants.
In The Blood of Olympus she, Nico, and Coach Hedge go on a quest to return the Athena Parthenos to Camp Half-Blood. While shadow-travelling to New York, the trio stops in San Juan and visits Reyna's former house, haunted by the ghosts of her relatives. There Reyna reveals that the Ramirez-Arellano family (which includes Roberto Cofresi and Captain Marion Frederic Ramirez de Arellano) has always been favored by Bellona. Reyna's father (an Iraqi war veteran) deeply loved the goddess, but his PTSD turned this love into an unhealthy paranoia. When Reyna was ten years old, he became a mania, or evil insane ghost. When the mania attacked Hylla, young Reyna picked up the closest weapon and killed what remained of her father. Reyna is reluctant to discuss the incident because patricide is "unforgivable" in New Rome.
Coach Gleeson Hedge
Gleeson Hedge is a satyr first mentioned in The Last Olympian, as the author of a distress call sent to Grover Underwood. Like Grover, Hedge is also a demigod Protector; his proudest "recruit" being Clarisse La Rue. He disguises himself as a coach at the Wilderness School to escort Piper McLean and Leo Valdez (and later, Jason Grace) to Camp Half-Blood. He also serves as the adult chaperone for the Argo II and later accompanies the Athena Parthenos to camp. Despite his often warlike and often overly aggressive attitude, Hedge is kind and understanding to campers in need. He enjoys extreme sports and martial arts movies. In The Lost Hero, Hedge falls in love with Mellie the cloud nymph (assistant to Aeolous) and marries her; by the time of The House of Hades, Mellie is pregnant with a satyr boy. Chuck, the baby, is born at the end of book five, with Clarisse as his godmother. In The Hidden Oracle, Hedge, Mellie, Chuck, Piper, and Jason are spending the winter in Los Angeles.
The Trials of Apollo main characters
In The Heroes of Olympus, Apollo's descendant Octavian promises the god many things for blessing his prophetic skills, which leads to the Olympians' distraction from the true threat of Gaea, and to the resurgence of Python. As a result, the Delphic Oracle ceases to function, effectively halting demigod quests, and Zeus punishes Apollo. Zeus's punishment consists of making Apollo mortal, though he retains most of his personality and some more minor powers. This punishment is revealed in The Trials of Apollo series.
Following a meeting with two thugs, Lester encounters a demigod called Meg McCaffrey who claims him as her servant until he regains his godhood. There, Apollo has to adjust himself to a life of mortality and questing to regain his former powers and lifestyle. Apollo is released by Meg after the revelation of her alliance with his enemy.
Lester is a 16-year-old teenager with curly brown hair, blue eyes, acne, and a flabby torso. He is narcissistic, prideful, and arrogant, but does his best to not be a burden on others. His mortal transformation has made him realize how miserable humans are in facing the gods. In particular, he grows to deeply care for Meg, and resolves to be with her despite the difficulties involved.
Margaret (Meg) McCaffrey is a 12-year-demigod daughter of Demeter and a main character in The Hidden Oracle. Her father was murdered by "the Beast" and she was subsequently adopted by Emperor Nero, unaware that the two are the same person. Nero taught her the arts of demigod and gave her a pair of crescent rings which can transform into sickles made of imperial gold, before giving her a task to lure Apollo into the Grove of Dodona. Meg appears to Apollo at an alley of Hell's Kitchen, Manhattan to defeat the thugs, also sent by Nero, to stage "robbery". Meg demands Apollo's servitude and with him travels to Camp Half-Blood with Percy's assistance. There, Meg displays unusual abilities even before Demeter claims her, and later goes with Apollo to search for missing demigods and the Grove in the nearby woods, having to endure a brief abduction in the process. Her relationship with Nero is revealed at the climax, but her growing doubtfulness regarding Nero's ways, not to mention her already familiar friendship with Apollo, leads her to rob Nero of his chance on burning the Grove. While she helps Apollo bring the Grove alive, she severs their bonding spell and leaves.
Meg is described as small and pudgy, with dark hair chopped in a messy pageboy style and black cat-eye glasses with rhinestones glittering in the corners. She is perky and adventurous, full of questions, and is also confrontational. She poses questions with no subtlety, something that Apollo is annoyed with but later comes to regard as a unique trait. Her abilities as Demeter's daughter allows her to connect better with nature as well as summoning a karpoi (crop spirit) called Peaches (a spirit of peach trees), a power that none of Demeter's other children demigods are known to possess.
Will Solace becomes the head of the Apollo cabin after the death of Michael Yew during the second Titanomachy. He is a native of Austin, Texas, the son of Apollo and an alt-country singer named Naomi Solace. In The Last Olympian, he uses his father's healing gift to help cure Annabeth. In The Blood of Olympus, Will is revealed to possess the ability to produce sonic waves in addition to his healing-related gifts. At the end of the series, it is implied that he begins a relationship with Nico. He refers to him as his boyfriend in The Hidden Oracle, after helping heal Lester.
Austin Lake is a teenage son of Apollo, an accomplished African-American musician, specializing in jazz saxophone. His mother, Latricia Lake, is a music professor at Oberlin College in Oberlin, Ohio whose music theory class Apollo once took. He is mentioned in The Last Olympian, where he is seen fighting alongside his brothers and sisters of the Apollo Cabin. He serves as a major character The Hidden Oracle, where his and Kayla's abductions in the woods by Nero prompt Apollo to rescue them. Austin's inherited talents are primarily musical.
Kayla Knowles is a daughter of Apollo first mentioned in The Last Olympian carrying out the orders of Michael Yew. She is a major character in The Hidden Oracle, and is abducted by Nero. Kayla's mortal father is a Canadian archery coach named Darren Knowles. Kayla's inherited gift is archery.
Harley is a son of Hephaestus, first seen in The Lost Hero. He is eight years old at the time of The Hidden Oracle, but very muscular. Harley has been trying to locate Leo, his older half-brother, with a magical beacon ever since his disappearance in the aftermath of the Second Gigantomachy.
Triumvirate Holdings is a company that is led by three beings who are said to be the worst Roman Emperors in history. They force other people to worship them. During the Second Titanomachy, Triumvirate Holdings was responsible for giving Luke Castellan and his allies with the Princess Andromeda, weapons, helicopters, and top human mercenaries. During the Second Gigantomachy, Triumvirate Holdings supplied Octavian with different weapons. Rachel Dare described Triumvirate Holdings to be so rich that they make her father's company "look like a kid's lemonade stand."
Among the known members of Triumvirate Holdings are:
- Emperor Nero - Emperor Nero is a legacy of Apollo and the main antagonist of The Hidden Oracle. The last in the Julio-Claudian dynasty, Nero is infamous for his tyranny and overindulgence in wealth and luxury with little regard to his subjects. He is the deified Roman Emperor, who has survived through the millennia along with two other deified Roman emperors—the Triumvirate. They have divided up North America and are attempting to control humanity through control of the major ancient oracles, including the Oracle of Delphi and the Grove of Dodona. He forms an alliance with Python, who holds Delphi, while he himself controls the other oracles and plans to destroy Dodona. Nero lives in New York, where he recruits and trains homeless demigods, and controls the eastern third of North America. He and the other two Roman Emperors have established Triumvirate Holdings. As "the Beast", Nero killed Meg's father, but later adopted and trained her in demigod arts so she could eventually lure Apollo into the Grove of Dodona. After Rhea restores the Grove of Dodona at Camp Half-Blood, Nero tries to force Apollo and Meg to burn the trees; failing at that, he sends a giant statue of himself, the Colossus Neronis, which originally stood in Rome, against Camp Half-Blood and Apollo and the Greek demigods defend the camp against it.
Though not all the gods who appear in Rick Riordan's novels are truly Olympians (that is, gods who live on Mt. Olympus), all Greek and Roman gods are generally considered to be a subset of the Twelve Olympians. As such, most characters in the series refer to these immortals generally as the "Olympian gods", to distinguish them from the Greco-Roman primordial gods and Titans.
- Zeus/Jupiter – The 1st Olympian and the King of the Gods, Zeus is most prominent in The Lightning Thief but has several roles throughout the rest of Percy Jackson & the Olympians. Zeus is shown prominently throughout the series to be extremely narcissistic, paranoid and a fierce hypocrite. In The Lost Hero, under the influence of Khione, Zeus forbids contact between gods and mortals and closes off Olympus (against the influence of Khione), although he indirectly helps the protagonists several times on their quests, such as answering his Jason's prayer for aid against Enceladus. As the primary Olympian god, his demigod children reside in Camp Half-Blood's biggest cabin, Cabin 1, although there is only one person who resides there at the end of The Heroes of Olympus: Jason. In the film adaption, Zeus is played by Sean Bean.
- Hera/Juno – The 2nd Olympian and the Queen of the Gods, she plays a role in The Titan's Curse, by helping Percy and the others on their quest in The Battle of the Labyrinth. As Juno in The Lost Hero, she is kidnapped by Gaea, and contacts Jason Grace to rescue her. Previously, as Juno, she had sneaked out of Olympus and switched Percy and Jason to try to unite the Roman and Greek demigods, going against the wishes of Zeus as part of a plan to defeat Gaea. Her cabin in Camp Half-Blood is Cabin 2, the second biggest in the camp, but because she does not have demigod children, it is empty. In the film adaptation, Hera is played by Erica Cerra.
- Poseidon/Neptune – The 3rd Olympian and the God of the Sea, Earthquakes, and Horses who is the brother of Zeus and Hades. In The Lightning Thief, he is suspected of having stolen Zeus's master bolt but is proven innocent after Percy recovers it from Ares. Poseidon fights Oceanus in the underwater front of the Titan war. He remains there in The Last Olympian while the other Olympians fight Typhon, until Percy convinces him that his power is necessary to defeat Typhon. He was last seen fishing for giant sea serpents on Long Island Sound outside Camp Half-Blood. Though he is referred to as Neptune in later books, he has yet to appear in Roman form. His cabin in Camp Half-Blood is Cabin 3, in which Percy is the sole permanent occupant. In the film adaptation of The Lightning Thief, Poseidon is played by Kevin McKidd.
- Amphitrite – The Wife of Poseidon. She appears in one scene of The Last Olympian and is described as a beautiful goddess wearing armor, with black hair and small horns like crab claws.
- Delphin – The God of Dolphins. Delphin is one of Poseidon's lieutenants in the war against Oceanus. He was seen briefly during a war council meeting in Poseidon's palace in The Last Olympian, in the shape of a dolphin.
- Palaemon – The God of Sharks. Palaemon is one of Poseidon's lieutenants in the war against Oceanus.
- Triton – Triton is a Sea God and Poseidon's "son and heir." He is depicted as a merman with two fishtails. He acts arrogant toward Percy but respects Tyson.
- Demeter/Ceres – The 4th Olympian and the Goddess of Agriculture. She thinks the answer to everything is farming-related. Demeter made few appearances in the Percy Jackson and the Olympians series. She and her daughter Persephone appear in The Last Olympian, where they participate in the battle against the Titans. Demetre's cabin in Camp Half-Blood is Cabin 4. In the film adaptation of The Lightning Thief, Demeter is played by Stefanie von Pfetten.
- Persephone/Proserpine – The Goddess of Springtime and Queen of the Underworld. Persephone is the wife of Hades and the daughter of Demeter and Zeus. Hades only allows her to visit Demeter, her mother, in the spring and summer. She is said to be able to "soften" Hades and make him more merciful. Unlike most minor gods, she sides with Olympus during the war against the Titans. In the film adaptation, Persephone is played by Rosario Dawson.
- Ares/Mars – The 5th Olympian and the God of War who is the son of Zeus and Hera and the father of Deimos, Phobos, Eros, Clarisse La Rue, and Frank Zhang (as Mars). Ares is a callous bully who is driven by either greed, aggression, violence or by the promise of violence. However, as Mars, he dislikes war without reason and is one of the more important Roman Gods. He is however still a bully and is all for killing the Greeks. Percy first encounters Ares in The Lightning Thief, in which he drives a large black Harley-Davidson motorcycle with flame decals and a leather seat made from human skin. Percy defeats Ares in a sword fight near the climax of the book. Cabin 5 in Camp Half-Blood is the home of Ares' demigod children; it is said to be surrounded by all kinds of warfare apparatus, including spikes. In the film adaptation of The Lightning Thief, Ares is played by Ray Winstone.
- Deimos – The God of Terror. A son of Ares, Deimos only appears in the short story "Percy Jackson and the Stolen Chariot" in The Demigod Files, where he torments Clarisse, forcing Percy and Clarisse to cooperate to defeat him.
- Phobos – The God of Fear. A son of Ares, Phobos only appears in the "Percy Jackson and the Stolen Chariot" story in The Demigod Diaries, where he torments Clarisse along with his brother. He has the power to show people their greatest fears, but Percy and Clarisse cooperate to defeat him. In The Blood of Olympus, a statue of Phobos is used by Piper to kill Mimas which fulfills the requirement of "one god and one demigod cooperating" in killing giants.
- Athena/Minerva – The 6th Olympian and the Goddess of Wisdom and Battle Strategy who is the daughter of Zeus and Metis. Athena first appears in The Titan's Curse, where she dislikes Percy and his relationship with her daughter, and votes to execute Percy due to his crucial role in the fate of Olympus. She then argues that it was the most logical and wise choice. As Minerva, she is a scatter brain and lost. She hates the Romans for reducing her to that and tells her descendants to kill the Romans. She also leads her best children to the Athena Parthenos, although Aphrodite believes it to be subconscious, as Athena doesn't know where it is. Her color scheme is grey, and her cabin in Camp Half-Blood is Cabin 6. In the film adaptation, Athena is played by Melina Kanakaredes.
- Apollo - The seventh Olympian and the God of the Sun, Light, Music, Truth, and Healing. He serves as a supporting character in Percy Jackson & The Olympians and The Heroes of Olympus series, and becomes the main protagonist of The Trials of Apollo series as a mortal named Lester Papadopoulos. Apollo first appears in The Titan's Curse, where he transports a group of demigods and Hunters at the behest of his sister Artemis. Later, he assists the quest group in rescuing Artemis from the Titans, even though doing so has been forbidden by Zeus. At the end of The Last Olympian, Apollo chooses Rachel Dare as his new Pythia. After the war in the second series, the furious Zeus punishes Apollo with mortality for his failure to identify Gaea as a threat. In the film adaptation of The Lightning Thief, Apollo is played by Dimitri Lekkos.
- Artemis/Diana – The 8th Olympian and the Goddess of the Moon, Wild Animals, Youth, and Hunting. Artemis is the daughter of Zeus and Leto and the twin sister of Apollo. Artemis, true to her vows, is a misandrist who discourages the companionship or value of men, and encourages maidenhood. As a result, she has no demigod children, but recruits Hunters who serve as her companions and attendants. Cabin 8 is her honorary home at Camp Half-Blood, but because she is a virgin, it is populated only when her Hunters come to visit. In the film adaptation of The Lightning Thief, Artemis is played by Ona Grauer.
- Hephaestus/Vulcan – The 9th Olympian and the Gods' Blacksmith. Hephaestus is the father of Charles Beckendorf and Leo Valdez. At Camp Half-Blood, Cabin 9 is dedicated to him. Hephaestus acts as a major ally of Percy in The Battle of the Labyrinth. In The Lost Hero, he defies Zeus by speaking to Leo through his dreams and he delivers the head of the mechanical dragon Festus for use as the figurehead for the Argo II. In the film adaptation of The Lightning Thief, Hephaestus is played by Conrad Coates.
- Aphrodite/Venus – The 10th Olympian and the Goddess of Love and Beauty. Aphrodite first appears briefly in The Titan's Curse. Her appearance shifts constantly, always becoming more beautiful. Cabin 10 at Camp Half-Blood is the home of her demigod children. In the film adaptation of The Lightning Thief, Aphrodite is played by Serinda Swan.
- Eros/Cupid – The God of Love who is the son of Aphrodite and Ares. In The House of Hades, Jason and Nico convinced Cupid to give them Diocletian's Scepter. He eventually gives it to them after Nico admits that he has feelings for Percy. Jason muses that he prefers Aphrodite's version of love to Cupid's love.
- Hermes/Mercury – The 11th Olympian and the Messenger of the Gods who is also the God of Travelers and Thieves. He is the son of Zeus and Maia. In the Percy Jackson and the Olympians series, Hermes helps Percy, hoping that he will be able to redeem Luke. All unclaimed demigods are packed into Hermes' cabin called Cabin 11 because Hermes welcomes all travelers.
- In the film adaptations, Hermes is played by Dylan Neal in the first film and by Nathan Fillion in the second.
- Dionysus/Bacchus – The 12th Olympian and the God of Wine and Parties who is the son of Zeus and Samele. Dionysus was made the head of Camp Half-Blood as punishment for pursuing "an off-limits wood nymph" romantically with it lasting for 100 years. Dionysus is portrayed as an extremely cynical and unfriendly misanthrope who does not appear to have much respect for other beings, except for Ariadne. He is a powerful god, but his powers are shown the least throughout the series. He has two demigod sons named Castor and Pollux, both of whom are the sole inhabitants of Cabin 12. Dionysus hates his job and has a low opinion of demigods, likening them to Theseus and his abandonment of Ariadne. In The Last Olympian following Kronos' defeat, Dionysus work at Camp Half-Blood is reduced to 50 years. Dionysus is played by Luke Camilleri in the first film and by Stanley Tucci in the second.
- Hades/Pluto – The unofficial 13th Olympian and the god of the Underworld. Hades, like Zeus and Poseidon, is considered an "elder god," one of the most powerful to be born of Kronos and Rhea. The eldest and most intelligent of the Big Three, Hades is an isolationist who distances himself constantly from other Gods because they do the same to him, primarily out of fear. They continuously underestimate Hades who is in fact a very honorable and fatherly individual. He is the father of Nico, Bianca, and Hazel. After the Second Titanomachy, Hades is granted Cabin 13, which is populated by his sole living Greek demigod child Nico. In the film adaptation of The Lightning Thief, Hades is played by Steve Coogan and is depicted as also having a fiery winged demon form.
- Hestia/Vesta – The Goddess of the Hearth and Home. She is simultaneously the oldest and the youngest of the Olympians, because she was the first-born of Kronos and Rhea, yet she was regurgitated from Kronos' belly the last. Like Artemis, Hestia swore the vow of chastity so no conflict can spring up about her allegiance; as a result, she does not have any demigod child. Hestia gives up her golden throne on Olympus to Dionysus/Bacchus in order to keep the peace on the Olympian counsel. She is the title character of The Last Olympian, wherein she helps Percy figure out how to defeat Kronos. She is described as preferring the shape of a young and softspoken, girl with brown hair. In Percy Jackson's Greek Gods, Percy speculates that Hestia may have helped Prometheus give fire to humans out of kindness.
Minor Greco-Roman gods
- Achelous – A River God with the face of a man and the head of a bull. He had previously fought with Hercules where Hercules removed one of Achelous' horns; his other horn plays a part in the plot of The Mark of Athena.
- Aeolus – The Master of the Four Winds. In The Last Olympian, he manipulates the winds to form a barrier around Olympus that protects it from air attacks from the Titans. In The Lost Hero, he is portrayed as frenetic and unbalanced by attempting to fill all the requests of the gods and hopes to be made god of the Wind. He hosts a weather report that airs every 12 minutes.
- Anemoi – The four Wind Gods.
- Boreas/Aquilon – The God of the North Wind. Boreas was first seen in The Lost Hero where Jason, Piper, and Leo ask for assistance. He has two immortal children called the Boreads and is the father of Khione.
- Khione – The Goddess of Winter who is daughter of Boreas and the sister of the Boreads. She first appears in The Lost Hero when she betrays Jason, Piper, and Leo to the forces of Gaea.
- The Boreads – The Boreads are the sons of Boreas and the brothers of Khione. Calais is depicted as a big simpleton who struggles with words that have more than two syllables while Zethes is shown to be heterosexual and to maintain an eighties hairstyle. In The Lost Hero, the Boreads are seen with Boreas. In The House of Hades, Khione and the Boreads attack the Argo II. The three of them are defeated when Piper McLean charmspeaks Festus to life.
- Notus/Auster – The God of the South Wind. He appears in The House of Hades.
- Zephyrus/Favonius – The God of the West Wind. He appears in The House of Hades.
- Boreas/Aquilon – The God of the North Wind. Boreas was first seen in The Lost Hero where Jason, Piper, and Leo ask for assistance. He has two immortal children called the Boreads and is the father of Khione.
- Anemoi – The four Wind Gods.
- Asclepius – The God of Healing who is the son of Apollo. The Lar Vitellius is a Legacy of Asclepius. In "The Blood of Olympus," Asclepius is first mentioned by Apollo on Delos, as the only person to have ever successfully cured death. Apollo gives Leo, Frank and Hazel his location in Epidaurus. Piper, Leo and Jason later meet Asclepius in the Asclepion. He quickly diagnoses Jason with myopia and gives him a pair of glasses. Later, he uses the Pylosian mint (the "cursed" daisy) and the Makhai to formulate the physician's cure and gives the trio instructions on its use.
- Bellona - The Roman Goddess of War. She is the mother of Hylla and Reyna. Though she is never seen in the series, she indirectly helps Reyna to kill the giant Orion by empowering her with her strength as mentioned in The Blood of Olympus.
- East River – A River God who personifies the river in New York. The East River only appears in The Last Olympian, where he sinks Titan ships coming to attack Olympus for half a sand dollar given to him by Percy. He is a rival of Hudson River.
- Elpis/Spes – The Goddess of Hope. She remains in Pandora's pithos as the only thing for humans to keep when other evils were released to the world. In The Last Olympian, the pithos is given by Percy to Hestia by the reasoning that hope remains the safest in hearth. In The Blood of Olympus, Gaea times her awakening to coincide with the Feast of Spes, a Roman festival honoring the goddess that falls on August 1.
- Eris – The Goddess of Chaos and the daughter of Nyx. In The House of Hades, Percy and Annabeth encounter Eris alongside Nyx and Eris' siblings near the Mansion of Night.
- Ganymede – The Gods' Cup-Bearer. He appears in The Sea of Monsters as part of a public service announcement advising users of the Gray Sisters' taxi service to use the seat belt. In Percy Jackson: Sea of Monsters, Ganymede is played by Richard Yearwood.
- Geras – The Goddess of Old Age and the daughter of Nyx (though Geras was actually a male in Greek mythology). In "The House of Hades," Geras is among the children of Nyx that encounter Percy and Annabeth near the Mansion of Night.
- Hebe – The Goddess of Youth who is the daughter of Zeus and Hera and the wife of Heracles. Hebe is among the minor gods who allied themselves with the Titans in the Percy Jackson and the Olympians series. After the war, she is awarded Cabin 18 in Camp Half-Blood for her demigod children.
- Hecate – The Titan-Goddess of Magic. Hecate is an ally of Kronos in the Percy Jackson and the Olympians series, but does support the gods against Gaea. Her empousai minions and her daughter Circe torment Percy in The Battle of the Labyrinth and The Sea of Monsters, respectively. After the Titans are defeated, she reconciles with Olympus and is granted Cabin 20 at Camp Half-Blood for her children. In The House of Hades, she helps Hazel defeat the giant Clytius.
- Hudson River – A River God who personifies the river in New York. Hudson River only appears in The Last Olympian, where he sinks Titan ships coming to attack Olympus for half a sand dollar given to him by Percy. He is a rival of East River.
- Hypnos - The God of Sleep, son of Erebus and Nyx and the father of Morpheus. He has Cabin 15 at Camp Half-Blood.
- Iris – The Goddess of Rainbows. Iris administers a network of rainbows, used by demigods and Olympians to communicate remotely. She is the mother of Butch, who makes a small appearance in The Lost Hero. After the Second Titanomachy, she is granted Cabin 14 for her demigod children. In The Son of Neptune, she meets Frank, Percy, and Hazel.
- Janus – The God of Gates, Doorways, Beginnings, and Endings. He appears as a minor character in The Battle of the Labyrinth. He has two faces, and each face seems to think the exact opposite of what the other face thinks.
- Kymopoleia – An oceanic goddess and a daughter of Poseidon. She is bethroted to Briares the Hekatonkheire, whom she resents. In The Blood of Olympus, Kymopoleia works with Polybotes to hinder the demigods while sailing through the Aegean Sea after feeling abandoned by her father. She is convinced by Jason to switch sides. Together, they kill Polybotes. She is nicknamed "Kym" by Percy.
- Lares – Household gods and ancestor spirits who are guardians at Camp Jupiter.
- Cato – A Lar. In The Son of Neptune, Cato was seen at the senate meeting where Frank Zhang is made a Centurion.
- Vitellius – A Lar who is a descendant of Asclepius. In The Son of Neptune, he was first seen when Hazel was introducing Percy to him.
- Morpheus – The God of Dreams who is the son of Hypnos. He is among the minor gods that appears as an ally of Kronos in The Last Olympian. He puts the entire city of New York to sleep during the battle.
- Melinoe – The Goddess of Ghosts. Melinoe lives in the underworld where her body is half chalky white, half pitch-black. She appears only in The Demigod Files in the short story "Percy Jackson and the Sword of Hades," where she scares people by showing them the ghosts of deaths they regret.
- Nike/Victoria – The Goddess of Victory. Leo Valdez, Hazel Levesque, Frank Zhang, and Percy Jackson meet her in "The Blood of Olympus". She is also on the Athena Parthenos in Athena's hand. Her children are in Cabin 17 at Camp Half-Blood.
- Nemesis – The goddess of vengeance and mother of the late Ethan Nakamura. After the Second Titanomachy, she is granted Cabin 16 for her demigod children. Nemesis is seen in The Mark of Athena where she makes a deal with Leo.
- Pan – The late god of the wild and patron of all satyrs. Pan has been missing for over 2000 years and the satyrs seek him fervently. After Percy and his friends find Pan in The Battle of the Labyrinth, he dies peacefully and releases his spirit to Percy, Grover, Rachel, and Annabeth.
- Pompona – The Roman Goddess of Plenty. Pompona isn't seen in person, but a statue of her speaks in The Last Olympian, becoming irritated when she is mistaken for Demeter by Percy, throwing bronze apples at Percy and Will Solace.
- Terminus – The Roman God of Boundaries. In The Son of Neptune, Terminus is portrayed as obsessive-compulsive and obsessed with order. He guards the city limits of New Rome. Terminus also helps Percy defeat the giant Polybotes.
- Thanatos – The God of Death. Thanatos is a lieutenant of Hades. In The Son of Neptune, the forces of Gaea capture Thanatos, allowing their dead allies to quickly return to life. He resumes his duties after being rescued by Percy, Hazel, and Frank.
- Tiberinus – A River God. Tiberinus appears to Annabeth in The Mark of Athena. He guides her to the beginning of the Roman leg of her quest for the Athena Parthenos. To Annabeth, he looks exactly like Gregory Peck.
- Rhea Silvia – Rhea Silvia is a former Vestal Virgin who mothered Romulus and Remus, the founders of Rome. She was made an immortal and wife of Tiberinus after she was given a death sentence for breaking her chastity vow. In The Mark of Athena, Rhea Silvia and Tiberinus give advice to Annabeth about the location of the Athena Parthenos. She is described as looking like Audrey Hepburn.
- Triptolemus – The God of Farming who is associated with Demeter. In The House of Hades, he cured Hazel and Nico from the poison of the Katoblepones after Frank obtained a serpent to repair his throne.
- Tyche/Fortuna – The Goddess of Luck. She is awarded Cabin 19 at Camp Half-Blood after the Second Titanomachy. Her Roman counterpart, Fortuna, is celebrated by Camp Jupiter in the "Feast of Fortuna" on June 24 every year to decide what fortune that would befall the camp.
The Primordial Deities are the deities that came before the Titans and the Olympians came into existence. Among the known Primordial Deities are:
- Gaia/Terra – The embodiment of Earth who is the primary antagonist of The Heroes of Olympus series. Gaia is the wife of Ouranos, and mother of the Titans, the Elder Cyclopes, the Hekatonkheires, the Giants, and Antaeus. She is the grandmother of the Olympians, whose rule she resents. As of The Son of Neptune, she remains sleeping in the ground, but retains some consciousness and influence. Like Kronos, she commands an army of mythological figures and monsters dissatisfied with the Olympians. During The Blood of Olympus, she is defeated by Leo Valdez, Piper McLean and Jason Grace who lift her into the sky, charm her to sleep and then incinerate her with a mighty blast of fire combined with a shot from an onager by Octavian. As a goddess she can't be killed, but like her son Kronos, her essence is scattered so much she hopefully will never able to form a consciousness again.
- Ourea – The Ourae are the primordial Gods of the Mountains who are the children of Gaia. In The House of Hades, there were some Ourae that make up the Apennine Mountains. When the Argo II tried to cross the Apennine Mountains, the Ourae there attacked them with boulders because the Ourae were loyal to Gaia. They hurled boulders from their mountaintops where they severely damaged the Argo II. Leo Valdez had to turn the Argo II away from the Apennine Mountains in order to come up with a different plan.
- Akhlys – The Goddess of Misery and a daughter of Chaos and Night. She is described as a miserable-looking old woman who carries the Aegis shield with Medusa's head carved into it. In The House of Hades, she offers the Death Mist to Percy and Annabeth, but later betrays them by luring them into Nyx's territory and trying to kill them with poison. In anger, Percy manipulates the poison back at Akhlys, causing her to run away in fear. This is the first time that Annabeth sees the darker part of Percy's personality.
- Keto – A Primordial Sea God in Greek Mythology and the sister of Phorcys. In The Mark of Athena, Keto appeared as a girl named Kate who is encountered in Phorcys' aquarium. When Gleeson Hedge discovered Phorcys' ruse, he freed Percy and Frank after knocking Kate out. After Percy, Gleeson, and Frank escape from the aquarium, Keto sent a skolopendra (shrimp monster-one of her children) after them.
- Nyx – The primordial Goddess of Night who resides at the Mansion of Night in Tartarus during the day. She is said to be the oldest being in the universe besides Chaos itself, and her residence, which is close to Chaos, is "worse than Medusa's head". In The House of Hades, Percy and Annabeth accidentally wander into Nyx's territory and try to pose as tourists guided by a brochure that does not mention Nyx. Angered, Nyx shows just how important she is and summons her children, who emit pitch-black darkness that even Nyx herself cannot see through it. Before she could catch them, the couple leave through the Mansion of Night. Nyx is described by Annabeth to be "as tall as the Athena Parthenos, but very much alive."
- Ouranos - The embodiment of the Sky who is the husband of Gaia and the father of the Titans. When Gaia gave birth to the Elder Cyclopes and the Hekatonkheires, Ouranos hurled them into the pits of Tartarus because of their ugly appearances. Kronos later castrated Ouranos before cutting him to pieces. Ouranos then cursed Kronos, stating that his child would come to overthrow him just as he had. Not much was mentioned about Ouranos afterwards. In Percy Jackson's Greek Gods, Percy Jackson described Ouranos to be tall and muscular with long dark hair and his skin changed depending on if it is day or night.
- Phorcys – A primordial Sea God and the brother of Keto. In The Mark of Athena, he and Keto run an aquarium in Georgia which contains a lot of rare sea monsters. Following a VIP tour, Phorcys traps Percy and Frank in a tank to fight each other. This attracts the attention of Gleeson Hedge, who manages to break the glass tank as they escape promising to return and free the sea creatures that Phorcys has in captivity.
- Tartarus – While Tartarus is the name of a location where the Titans were imprisoned, there is a primordial god by that name as well. Through Gaia, Tartarus fathered Typhon and the Giants. His real form is the whole Tartarus itself, but he personifies himself in a form that stands several feet tall with a face of a swirling vortex and a voice that makes it seem going inward, rather than outward. In The House of Hades, the personification of Tartarus appeared in physical form where he makes a remark about Gaia's awakening. Percy and Annabeth fought Tartarus until Iapetus and Damasen sacrificed themselves so that Percy and Annabeth could get out of the Underworld.
The Titans are the children of Gaia and Uranus. Most of them fought against the Gods during the Titanomachy which ended with the Gods winning. Among the featured Titans are:
- Kronos/Saturn – The Titans' greatest king and Lord of Time, which he can manipulate. Kronos is the main antagonist of the Percy Jackson & the Olympians series. He is the father of all the elder Olympians, as well as Chiron. He fights with a scythe with a six-foot-long magical blade that can harm both gods and mortals, once used to dismember his father Uranus. Kronos is initially trapped in Tartarus, but eventually escapes to possess the body of Luke Castellan. In this form, he personally leads the Titan army against Olympus. He is finally defeated by his own host, in fulfillment of the first Great Prophecy. In Percy Jackson: Sea of Monsters, Kronos is voiced by Robert Knepper. He was shown to have a gigantic, demonic body along with superhuman strength and the ability to use parts of his own body as projectile weapons.
- Rhea - The Queen of the Titans and the Titaness of Motherhood. As Kronos's wife, she was the mother of the elder Olympians. Unlike Kronos, Rhea loved the children that she gave birth to and even kept Zeus from being eaten. When it came to the Titanomachy, Rhea advised her nephews and nieces to remain neutral. Since Kronos' defeat, Rhea retreats to Upstate New York, but continues to keep in touch with her children. In The Hidden Oracle, Apollo learns that an oracle that Rhea created called the Grove of Dodona is the only one yet to be conquered by Nero. Rhea subsequently appears to Apollo to offer him advice. She is a hippie and has attended Woodstock.
- Aigaios – Aigaios is a partner of Oceanus who assists in the Titans' War against Poseidon. In The Titan's Curse, Tyson reports that Aigaios protected the Princess Andromeda (a cruise ship carrying the Titan Army) from Poseidon's wrath.
- Atlas – The general of the Titan army. He is the father of Calypso and the five Hesperides. Atlas was imprisoned on a mountaintop near San Francisco, forever cursed to hold up the sky. He is extremely powerful and strong, even for a Titan. He served as the primary antagonist in The Titan's Curse, but is mocked by the other Titan's in later books for his failure. He does not participate in Kronos's final assault.
- Hyperion – Titan of the East. Hyperion is the father of Helios and Selene, the Titans of the sun and moon, respectively. He appears in The Last Olympian, where he is clad in full golden armor and battles Percy. He has all the powers of the Sun. Grover Underwood traps Hyperion by turning him into a tree. In The House of Hades, Hyperion is stopped from reforming in Tartarus by his brother Iapetus (Bob the Titan). He and Krios are seen later guarding the Doors of Death. Both are obliterated by the physical form of Tartarus as a show of power..
- Iapetus/Bob the Titan – Lord of the West. First seen in The Sword of Hades, when Percy drags him into the river Lethe, erasing his memory. Rather than kill him, Percy renames him "Bob" and sends him to work for Hades. In The House of Hades, he helps Percy and Annabeth escape Tartarus because of Nico di Angelo's kind description of Percy. Annabeth is afraid that he will regain his memories by meeting with his fellow Titans, but Iapetus continues to help them and later sacrifices himself to fend off Tartarus while the use the Doors of Death. In the outside world, Percy fulfills Iapetus' final wish by looking at the stars and saying "hello" for the Titan. Bob befriends a small sabre cat while in Tartarus, as well as the giant Damasen.
- Koios – Lord of the North. In The House of Hades, Koios is briefly seen in Tartarus. He mentions that his daughter Leto had been mistreated by Zeus after "she bore him those fine twins" (a reference to Apollo and Artemis). Percy describes Koios as having Apollo's smile and Artemis's eyes.
- Krios – The Titan of Stars and constellations and Lord of the South. Percy first sees Krios in a dream during The Last Olympian. He wears armor decorated with glowing stars. In The Lost Hero, Jason claims to have defeated Krios in single combat on Mount Othrys. In The House of Hades Krios is seen with Hyperion guarding the Doors of Death. Both of are obliterated by Tartarus's physical form.
- Oceanus – The Titan of the Ocean. Oceanus is depicted as having the upper body of a muscular man with a long beard and horns and the lower body of a serpent. He did not fight the Olympians in the original Titanomachy, but in The Last Olympian, he assaults Poseidon's forces underwater. Oceanus is incredibly powerful and his intense battle with Poseidon lasts for days and creates storms and tsunamis. After the defeat of Kronos, Oceanus escapes back to the depths of the ocean.
- Prometheus – The Titan of Forethought. Like Oceanus, Prometheus prefers to fight for the more powerful side. He supported the Olympians in the first Titanomachy but joins with Kronos in the second, in part because of Zeus's cruel punishment for Prometheus's gift of fire to mankind. This punishment ended only with the hero Hercules—a fact Prometheus uses to justify his claims to love heroes. He is sent to negotiate Percy and Thalia's surrender during the Battle of Manhattan, offering them the spirit of Elpis (goddess of hope). He flees after Kronos's defeat, sending a list of excuses to Mount Olympus.
The Gigantes (also known as the Great Giants) are a race of giant beings that were made by Gaia and Tartarus to overthrow Olympus. They were previously defeated by the Gods and Heracles during the Giantomachy. Each was meant to oppose a specific god. They can only be defeated by a god and heroes working together. They are mostly described as very tall with dragon-like legs and shaggy hair with different objects braided into it.
- Alcyoneus – A 40 ft. Gigantes with rust-colored dragon-like legs whom Hazel almost resurrects during World War II. Alcyoneus eventually rises in the The Son of Neptune. He is invincible so long as he remains in his homeland which after his resurrection is Alaska. Frank, Hazel, and Arion defeat him after driving him into Canada. He opposes Hades/Pluto.
- Clytius – A 20 ft. Gigantes with ash-colored dragon-like legs. He opposes Hecate. Clytius appears in The House of Hades. He guards the living side of the Doors of Death in Epirus. He is defeated by Hecate, Jason, Leo, Piper, Nico, Frank and Hazel.
- Damasen – A 20 ft. peaceful Gigantes with red dragon-like legs who appears in The House of Hades and is exclusive to the series. He had been made to oppose Ares/Mars. Damasen had been exiled to Tartarus as he was peaceful not violent and for refusing to take part in the ancient fight against the gods and Hercules. Percy and Annabeth encounter him in Tartarus when Iapetus (Bob) brings them to his lair. When the personification of Tartarus arrives near the Doors of Death, Damasen confronts him with Iapetus so that Percy and Annabeth can escape back to the living world.
- Enceladus – A 30 ft. Gigantes with green dragon-like legs. Enceladus was the first Giants to be reawakened in the Heroes of Olympus series. He opposes Athena/Minerva. In The Lost Hero, Enceladus is killed by Jupiter and Jason as the Giants can only be killed by a god and a hero working together. In The House of Hades, Enceladus re-enters the world through the Doors of Death.
- Ephialtes and Otis – Ephialtes and Otis are twin 12 ft. Gigantes that look somewhat more human than most of their brothers since they each have two snakes for legs (which they usually conceals under their black pants). They both oppose Dionysus/Bacchus. Ephialtes and Otis are awakened in The Mark of Athena by Gaea. Ephialtes and Otis manage to capture Nico di Angelo and were tasked by Gaia to kill all demigods of prophecy but two, whom they are to bring to her. They fight Jason and Percy who defeat them with the help of Bacchus. In The House of Hades, Ephialtes and Otis they return to the living world through the Doors of Death.
- Hippolytos – The 30 ft. Messenger of the Gigantes with orange dragon-like legs. He opposes Hermes/Mercury. Hippolytos makes a minor appearance in The Blood of Olympus.
- Mimas – The 25 ft. Gigantes charcoal-colored dragon-like legs. He opposes Hephaestus/Vulcan. Mimas makes a minor appearance in The Blood of Olympus.
- Orion – A 20 ft. Gigantes who doesn't sport dragon-like legs and is much different from the Orion of Greek Mythology as he opposes Apollo and Artemis/Diana and is exclusive to this franchise. In The Heroes of Olympus, Orion is sent by Gaea to hunt down Nico di Angelo, Reyna Avila Ramírez-Arellano, and Gleeson Hedge throughout their journey. He nearly catches them numerous times, but they either shadow travel away before he has the chance or are saved by allies (such as the Hunters of Artemis and Amazons). Orion murders countless Hunters and Amazons, including Phoebe, but escapes with his life. Much later, Reyna impales him through the hear with her dagger.
- Periboia – The female Princess of the Gigantes who is Porphyrion's daughter. She opposes Aphrodite/Venus. Periboia appears in The Blood of Olympus.
- Polybotes – A 30 ft. Gigantes with Komodo dragon-like legs. He opposes Poseidon/Neptune and can turn water to poison. Polybotes attempts to destroy Camp Jupiter in The Son of Neptune with an army of monsters. He is killed by Percy and Terminus. He expresses a particular desire to capture Percy and make him watch as he kills Poseidon. In The House of Hades, Polybotes returns to the living world through the Doors of Death.
- Porphyrion – The 40 ft. King of the Gigantes with green dragon-like legs that are described to be the same color as lima beans. He opposes Zeus/Jupiter. Awakened in The Lost Hero, Porphyrion fights Jason and his friends. Hera almost kills him, but he escapes.
- Thoon – A shriveled wizened Gigantes with white dragon-like legs. He opposes the Fates. Thoon makes a minor appearance in The Blood of Olympus.
The following demigod characters all have one parent who is a Greek or Roman god (or, more rarely, a Titan), while the other parent is a mortal human. It is common for these "half-bloods", as they are known, to grow up unaware that they are not entirely human. They are frequently referred to by gods and other mythological beings as "mortals", though they are certainly more than human.
- Alabaster Torrington – Alabaster appears in the short story "Son of Magic" in The Demigod Diaries. He is the son of Hecate and half-brother of the murderous monster Lamia. Alabaster was one of the demigods who allied with Kronos in the Titan War in The Last Olympian. He was sent into exile after the Titan War after refusing to stay at Camp Half-Blood. He claims to have led his siblings to their deaths during the war against the Olympians. He has several magical powers, which he channels through spells and magic writings.
- Alice Miyazawa – Alice is a daughter of Hermes. She is a close friend of Julia, and the two are always never far from each other. Chiron states that she and Julia have taken over the Stoll brothers' knack for mischief, following Travis' enrollment on college and Connor's sudden reservement that it caused. The two girls harbor a crush on Apollo.
- Bianca di Angelo – Bianca is a twelve-year-old daughter of Hades and the older sister of Nico di Angelo. She becomes a Hunter of Artemis, whom she attempts to rescue in The Titan's Curse, alongside Percy, Grover, Thalia, and Zoë. She sacrifices herself to save the group from a mechanical prototype of Talos. For a while, this causes Nico to resent Percy, who had promised to do his best to protect Bianca. In The Battle of the Labyrinth, Bianca (as a spirit) helps Nico learn to forgive Percy. Later in The Son of Neptune, she tries for rebirth on the Isle of the Blest.
- Billie Ng – Billie is a daughter of Demeter. In The Hidden Oracle, Billie is the only demigod of the Demeter cabin left in the winter season after the disappearance of her counselor, Miranda, until the arrival of Meg. She points out Meg's parentage during her claiming, in which a sickle and grain, symbols of Demeter, glow above her head.
- Bobby – Bobby is a caregiver of Camp Jupiter's war elephant Hannibal, first mentioned in The Son of Neptune. His Olympian parent is unknown.
- Butch – Butch is the head counselor of the Iris cabin at Camp Half-Blood. He and Annabeth are the ones who bring Jason, Piper and Leo to the camp at the beginning of The Lost Hero. He is bald and muscular, with a tattoo of a rainbow on his upper arm.
- Castor – Castor is a son of Dionysus and the twin brother of Pollux (both of whom are named after the Gemini). He is killed in The Battle of the Labyrinth when he was stabbed by a demigod allied with Kronos.
- Cecil Markowitz – Cecil is a son of Hermes. In The Blood of Olympus, he is a part of the team sent to sabotage Camp Jupiter's onagers. In The Hidden Oracle, Cecil is the first to kidnapped by Nero and strapped to a crucifix to be sacrificed to burn the Grove of Dodona, although Apollo and Meg manage to save him.
- Charles Beckendorf – Charles Beckendorf is a son of Hephaestus. Like his father, he is a master smith. He is African American. He was in a relationship with Silena Beauregard, and is described as Mrs. O'Leary the hellhound's best friend next to Percy. He dies during an assault on the Princess Andromeda with Percy in The Last Olympian, around the age of 18. He had plans to attend NYU in the fall.
- Chiara Benvenuti – Chiara is a daughter of Tyche. She is Italian and indulges in the language when she curses, which Apollo understands much to his dismay. She has a rivalry with Damien, but is shown to be close friends otherwise. Apollo has more than once expressed his interest on her, though he does it with Damien also.
- Chris Rodriguez – The son of Hermes. He is often described as wearing a bandana around his head. Chris had joined Kronos and the Titans, but was turned insane by the ghost of Minos while on a mission in the Labyrinth. Clarisse finds him and brings him to Camp Half-Blood, where Dionysus restores his sanity. Chris later has a relationship with Clarisse. In the film adaptation, Chris is played by Grey Damon.
- Clovis – Clovis is the lead counselor of the Hypnos cabin. In The Lost Hero, Annabeth consults him regarding Jason's memory loss. In "The Blood of Olympus", Nico Di Angelo sends a dream message to him to contact Thalia Grace.
- Connor Stoll – Connor and his brother Travis serve as lead counselors of the Hermes cabin after Luke's departure. The Stolls are known to be crafty and mischievous, like their father. They are tall and thin, with stringy brown hair. Both survive the Titan war. In The Hidden Oracle, Connor becomes the sole counselor due to Travis attending college, something that he still has not gotten over with. He picks on Meg after the latter pokes him in the eyes.
- Dakota – A son of Bacchus at Camp Jupiter, Dakota has an addiction to extra-sugary Kool-Aid. He is both a centurion of the Fifth Cohort and a senator. Dakota is often on a sugar high, especially when stressed; in moments of clarity, however, he proves himself a capable leader.
- Damien White – Damien is a son of Nemesis. He has a heated rivalry with Chiara Benvenuti, although Apollo hints that the two are in a relationship at the end of The Hidden Oracle.
- Drew Tanaka – Drew is the lead counselor of the Aphrodite cabin, succeeding Silena, in The Lost Hero. She bullies and controls her cabin members with her power of charmspeak, leading Piper to successfully challenge her for the lead counselor position. She is also mentioned in The Serpent's Shadow of The Kane Chronicles as someone Sadie hates.
- Ellis Wakefield – Ellis is a son of Ares. In The Hidden Oracle. he is the second demigod to be kidnapped by Nero in the woods of Camp Half-Blood. Apollo later frees him and the others.
- Ethan Nakamura – A son of Nemesis, Ethan fights with Kronos and the Titans but begins to rethink his position. In The Last Olympian, he learns Percy's Achilles weak spot, but instead of killing him, Ethan turns on Kronos. However, his attack fails and Kronos kills him. Before he falls to his death 500 feet from Olympus, Ethan tells Percy that none of the bad blood that led to the war would have been caused if the minor gods had thrones on Olympus.
- Gwendolyn (Gwen) – A centurion of the Fifth Cohort at Camp Jupiter. Gwendolyn is killed in The Son of Neptune but comes back to life because of Thanatos's capture. Her return prompts Mars to appear at Camp Jupiter and explain the circumstances of Thanatos's absence. She retires as centurion the day after and is replaced by Frank Zhang.
- Holly and Laurel Victor – Holly and Laurel are a pair of sisters and daughters of Nike. As per their upbringing, they are very competitive and refuse to be made second, hence why they are placed as co-counselors of the Nike's cabin, otherwise, as Kayla puts it "they would've taken over the camp by now and proclaimed a dictatorship". Apollo describes them as looking like the "gorgeous, ferociously athletic African nymphs" that he and Artemis used to hang out at Lake Tritonis.
- Jacob – Jacob is the legion Aquilifer (which is an eagle bearer) of Camp Jupiter. His godly parent is unknown.
- Jake Mason – Jake becomes the head of the Hephaestus cabin after the death of Beckendorf in The Last Olympian. He is severely injured during the Hepheastus's cabin's attempt to tame the bronze dragon later named Festus. In The Lost Hero, he steps down and gives the lead counselor position to Leo, after Leo finds Hephaestus's bunker in the woods.
- Jason – Not to be confused with Jason Grace or the mythical Jason, he is a demigod briefly mentioned in "The Titan's Curse", being instructed by Thalia to team with Silena Beauregard and Laurel during capture the flag. His godly parent is unknown.
- Julia Feingold – is a daughter of Hermes. Like her best friend, Alice, she harbors a crush on Apollo.
- Katie Gardner – Katie is the head counselor for Demeter's cabin at Camp Half-Blood after the war with the Titans. Katie strongly dislikes the Stoll brothers, who once put chocolate Easter bunnies on the Demeter cabin's grass roof.
- Lacy – Lacy is a daughter of Aphrodite who befriends Piper in The Lost Hero. She also appears in The Kane Chronicles. Lacy and Drew Tanaka appear in the Kane Chronicles, where Lacy is familiar with main character Sadie Kane.
- Larry – A senator at Camp Jupiter and a member of either the First or Second Cohort.
- Laurel – Laurel is only mentioned in The Titan's Curse. Because of circumstances around her mention, she may be a daughter of Aphrodite.
- Lee Fletcher – Lee was the head of Apollo cabin. He leads a team to attack a dragon threatening the camp. He is killed by a giant in The Battle of the Labyrinth.
- Leila – Leila is a daughter of Ceres and a centurion of the Fourth Cohort. In The Blood of Olympus, she and the rest of her cohort defect to Reyna's side once the latter arrives at Long Island.
- Lou Ellen – Lou Ellen is a daughter of Hecate in The Lost Hero. She is known for playing magical tricks on fellow campers.
- Malcolm Pace – Malcolm Pace is the assistant counselor of the Athena cabin, under Annabeth.
- Michael Kahale – Michael Kahale is a son of Venus and a centurion of the First Cohort. He is described as a fearsome Hawaiian despite being the son of a love goddess. In The Blood of Olympus, he reluctantly follows Octavian's order to attack Camp Half-Blood, but later leaves him to his fate when the latter ignites an onager with his feet being tangled with it.
- Michael Varus – Michael Varus was a son of Janus and a former praetor of Camp Jupiter in the 1970s. He was killed by Alcyoneus during an expedition in Alaska and the eagle of Camp Jupiter was stolen with him. This tarnished the reputation of Varus' cohort, the Fifth, which was not recovered until Jason's promotion to praetor over three decades later. Varus' ghost appears to attack Percy in The Son of Neptune and again in The Blood of Olympus where he confronts Jason with his mother's mania and then mortally wounds him with an imperial gold sword.
- Michael Yew – Michael Yew succeeds Lee Fletcher as head of the Apollo cabin. He is described as very short, with a face that reminds Percy of a ferret. In The Demigod Files, in an interview with Clarisse, she mentions that she would want to pulverize Michael, thus stating that they are enemies. He is an excellent archer like most of Apollo's children and uses sonic arrows which were given to him by his father. He was presumed killed after leading a group of demigods in the fight against Kronos's army; Percy found his bow, but not his body.
- Miranda Gardiner – Miranda is second in command of the Demeter cabin in The Lost Hero. She assumes the head counselor's duties in the winter when Katie Gardner hibernates. In The Hidden Oracle, Miranda is the third to be kidnapped during Nero's spree in luring Apollo, which greatly disturbs Chiron due to her important status as counselor, though Apollo manages to rescue her. She is dating Sherman.
- Mitchell – Mitchell is a son of Aphrodite who is a friend of Piper in The Lost Hero.
- Nyssa Barrera – Nyssa is a daughter of Hephaestus. She meets Leo in The Lost Hero. She is mentioned on several occasions in the beginning and end of The Lost Hero. She also helps plan out Harley's Three-Legged Death Race in The Hidden Oracle.
- Paolo Montes – Paolo is a son of Hebe. He is from Brazil and is only able to speak Portuguese, although he understands English. He is able rejuvenate himself after particularly serious injuries, an ability which he inherited from his mother.
- Pollux – Pollux is a son of Dionysus and the twin brother of Castor (both of whom are named after the Gemini). He survives the war against the Titans, though his brother dies in The Battle of the Labyrinth.
- Sherman Yang – Sherman is a son of Ares. He is left in the care of his cabin as Clarisse, the counselor, is attending university. He marks Meg for target after the latter kicks him in the crotch, together with Connor. Like the other children of Ares, he is easily provoked. He is dating Miranda.
- Silena Beauregard – Silena was the head of the Aphrodite cabin for most of the Percy Jackson & the Olympians series. She is kind to Percy and befriends Clarisse LaRue after giving the other girl advice about her first relationship. She served as a spy for Kronos within Camp Half-Blood, but wanted to quit when her actions led to the death of her boyfriend Charles Beckendorf. Luke blackmails her into continuing as a spy. In The Last Olympian, she redeems herself by disguising herself as Clarisse and leading the Ares cabin into battle against the Titans. She dies a hero's death and is given a funeral at camp.
- Travis Stoll – Travis and his brother Connor serve as lead counselor of the Hermes cabin after Luke's departure. The Stolls are known to be crafty and mischievous, like their father. He and his brother survive the Titan war. In The Trials of Apollo: The Hidden Oracle, he is shown to have gone to college, leaving his brother at camp.
- Valentina Diaz – Valentina is a daughter of Aphrodite and the only member of her cabin left during winter season in The Hidden Oracle.
In this franchise, different historic people are mentioned to have Greek Gods as their parents or are otherwise involved with the series. Among the known historical demigods are:
- Adolf Hitler – Adolf Hitler is a son of Hades and the chancellor of Nazi Germany. He is mentioned as one of the demigods of the Big Three who caused World War II, which resulted in the Pact of the Big Three.
- Alfred Hitchcock – Alfred Hitchcock is the son of an unknown god. Alfred is mentioned when Percy Jackson and Will Solace arrive at the Plaza Hotel. It says that the Plaza attracted a lot of famous demigods over the years, such as the Beatles and Alfred Hitchcock.
- Amelia Earhart – Amelia Earhart is the daughter of an unknown god. In The Sea of Monsters, Annabeth Chase mentions Amelia when talking to Circe. She was among the list of great female heroes. In "The Lost Hero," Aeolus mentions that he knocked Amelia Earhart out of the sky and that the gods still pester him about it while talking to Jason Grace, Piper McLean, and Leo Valdez in his fortress.
- Archimedes – Archimedes is the son of Hephaestus. He is credited with the creation of many modern machines and an accurate approximation of pi. He is in modern times considered as one of the most well-known and one of the greatest of Hephaestus' children. It is the wish among many of Archimedes' modern-day siblings to find the lost works of Archimedes. During the Second Punic War, Archimedes was killed by a Roman guard working for General Marcus Claudius Marcellus who had given specific orders not to harm Archimedes. While searching for Nico di Angelo with Frank Zhang and Hazel Levesque in Rome as seen in The Mark of Athena, Leo Valdez recovered the lost works of Archimedes. He uses them to destroy the eidolons, possessive spirits working for Gaea. He planned to take them to Bunker 9 at Camp Half-Blood to study them further. With Archimedes' works, Leo hoped to save Camp Half-Blood from the Roman forces from Camp Jupiter.
- Banastre Tarleton - Banastre Tarleton is mentioned as a demigod son of Bellona who participated in the Battle of Waxhaws. According to Reyna, Tarleton ignored the Colonial leader Abraham Buford's white flag and his forces massacred Buford's men. It is also mentioned that he was one of many Roman demigods who fought for the British during the American Revolution while the Greeks fought for the colonists.
- Blackbeard – Edward "Blackbeard" Teach is the son of Ares. He was a notorious English pirate who operated around the West Indies and the Eastern coast of the American Colonies during the early 18th century. Instead of dying in his famous last stand, his ship landed on Circe's island where he and his crew were turned into guinea pigs for several hundred years. In The Sea of Monsters, Edward Teach is seen in guinea pig form. While on a quest, Annabeth Chase used Hermes' multivitamins to turn all of the guinea pigs, among them Percy and Edward, back into humans. Along with his crew, he began to chase after Circe while Percy and Annabeth escaped with their pirate ship, the Queen Anne's Revenge. He was last seen on Circe's island yelling at Percy Jackson and Annabeth for stealing his ship.
- Franklin D. Roosevelt – Franklin D. Roosevelt is the son of Zeus and former President of the United States. He was mentioned by Bianca di Angelo in The Titan's Curse when she was trying to name the previous president due to her long period of time in the Lotus Casino.
- Frederic Bartholdi – Frederic Bartholdi is the son of Athena who designed the Statue of Liberty. In The Demigod Files story titled The Stolen Chariot, Percy Jackson mentions Frederic Bartholdi to Clarisse La Rue. According to what Annabeth Chase had told Percy, Bartholdi designed the Statue of Liberty as a representation of his mother Athena.
- George Washington – George Washington is a son of Athena and is the 1st President of the United States. In The Lightning Thief, George Washington is mentioned in the book as one of the few famous and successful demigods who survived outside of Camp Half-Blood and is depicted in one of the works displays during the Camp Half-Blood fireworks.
- Harriet Tubman – Harriet Tubman is a daughter of Hermes and an abolitionist spy. In The Battle of the Labyrinth, Chiron states that Harriet once used many clear-sighted mortals on the Underground Railroad hinting that the Underground Railroad may have utilized the Labyrinth to help transport escaped slaves.
- Harry Houdini – Harry Houdini is the son of an unknown god who is a famous magician and escape artist, perhaps implying that his father was Hermes. It is mentioned in The Lightning Thief that he, Orpheus, and Hercules have each been able to escape from the Underworld. A Nereid said that Houdini "could escape even the depths of Tartarus."
- Jack London – Jack London is the son of Mercury and author of Call of the Wild. He was mentioned in The Lost Hero as the one who built the Wolf House where Lupa judges the newly arrived demigods to see if they are worthy of being trained at Camp Jupiter.
- Joshua Lawrence Chamberlain – Joshua Lawrence Chamberlain is the son of an unknown god and a soldier in the American Civil War. In The Sea of Monsters, Chamberlain is mentioned by Chiron when talking to Percy Jackson after having rescued him and his friends from the Princess Andromeda.
- Thomas Jefferson – Thomas Jefferson is the 3rd President of the United States and the writer of the Declaration of Independence. In The Battle of the Labyrinth, Thomas Jefferson is mentioned to be among the rotating members of the Judgement Pavilion where he is assigned to judge where Daedalus will be sent to after his death.
- William H. Seward – William H. Seward is the son of Hebe and a former Governor of New York. During the Battle of Manhattan in The Last Olympian, Annabeth Chase activated a statue of William H. Seward in Madison Square Park. It was the first statue she activated. It was a celestial bronze statue on a red marble pedestal. The William Seward statue was sitting on a chair, legs crossed, wearing an old-fashioned suit (similar to Abraham Lincoln's suit) and a bow tie and long coattails. Books were piled under his chair, and he held a writing quill in one hand, big metal sheet of parchment in the other. The statue was one of many that Daedalus had created, to either attack or defend the Olympian gods, depending on which he needed to do to survive. He continued waking the other automatons as he was instructed to do.
- William Shakespeare – William Shakespeare is the son of Apollo. In The Battle of the Labyrinth, William Shakespeare is one of the rotating members of the Judgement Pavilion.
- William Tecumseh Sherman – William Tecumseh Sherman is a son of Ares who fought in the American Civil War. In The Mark of Athena, William Sherman was mentioned by Coach Hedge when he and the seven arrived in Atlanta calling him Frank Zhang's half-brother and mistaking the son of Mars as Greek.
- Winston Churchill – Winston Churchill is the son of Poseidon who was the Prime Minister of the United Kingdom.
The following are mentioned not as direct children of the Olympians, but as grandchildren, great-grandchildren, or the like:
- Bryce Lawrence – A legacy of Orcus. In The Blood of Olympus, Bryce is seen by Nico di Angelo in a dream. Despite being banished from Camp Jupiter by Reyna years ago for having killed his own centurion, Octavian allows him to return turning a blind eye to his cruelty towards the rest of his fellow cohort when he first joined the legion. He is given his probatio necklace and is assigned to the Fifth Cohort. In South Carolina, Bryce overhears Reyna's story of killing her father, and tries to capture her and take her to Octavian to charge her with the crime of patricide. He then is turned into a ghost by Nico and forced into the Underworld.
- Emily Zhang – Emily is Frank's mother, a Canadian Forces soldier who died in Afghanistan. She is descended from Periclymenus, which imbues her with the ability to shapeshift. After her death, her mother raises Frank. She only appears in flashbacks.
- Grandma Zhang - Emily's mother, also with her family's gift. She believes Frank should spend more time studying his Chinese heritage.
- Julia – A little girl who is the descendant of an unspecified god. In The Son of Neptune, she works as Terminus' helper at the security checkpoints at the New Rome town line. She often hides playfully underneath Terminus' statue base.
- Octavian – Octavian is ambitious and cunning. He describes himself a descendant of Apollo in The Son of Neptune but Rachel calls him "son of Apollo" in The Mark of Athena. He reads the auguries for Camp Jupiter. After Jason Grace disappears, he campaigns to succeed to Jason's position as praetor. He is suspicious of the amnesic Percy Jackson when he arrives at Camp Jupiter, deducing he is a Greek demigod, rather than Roman. Mocking him and attempting to undermine his quest. When demigods from Camp Half-Blood arrive at Camp Jupiter, Octavian declares the Greeks invaders and urges the Romans to fight them off, believing the Greeks to be in league with Gaea. His warmongering escalates further in The House of Hades where he violates direct orders from Reyna not to attack Camp Half-Blood after leave him in command of the Legion. He is thin and blonde. He is also said to "look eighteen but could probably pass as younger." He dies in The Blood of Olympus where he launches an onager attack on Gaea during her defeat. His foot gets tangled in the launching rope and he is launched along with the payload and dies in the explosion. As his effort may have helped defeat Gaea, Octavian is hailed as a hero and his true actions covered up.
The following characters from Greek mythology appear in this series. Most of them are the direct children of gods or Titans, but a few are mortals with such great power that they are able to influence the realm of the gods.
- Achilles – The son of Thetis and Peleus. The ghost of Achilles appears briefly in The Last Olympian, warning Percy about the Curse of Achilles.
- Calypso – Calypso is the daughter of the titan Atlas who is imprisoned on the island of Ogygia for supporting her father during the first titan war. She first appears in The Battle of the Labyrinth, where she nurses Percy back to health. She falls in love with Percy and is heartbroken when he leaves. Percy asks the gods to release her at the end of The Last Olympian, but she is still residing there of The House of Hades, when Leo becomes trapped on Ogygia. She ends up falling in love with him. After Leo escapes, he swears that he will return for Calypso. At the end of The Blood of Olympus, Leo gets back to Ogygia and frees Calypso. They then soar into the unknown on the back of the mechanical dragon Festus. In The Hidden Oracle, Calypso comes to Camp Half-blood with Leo and reveals that, due to her choice to leave Ogygia, she has become a mortal. She seems to dislike Apollo's company due to a past relationship that went awry, although she has to accompany him on his trials, together with Leo.
- Charon – Charon is the ferryman who carries the dead across the river Styx to the underworld. Percy and his friends meet him in The Lightning Thief. He also states he does not like being confused with the centaur Chiron. He likes Italian suits. In the film adaptation, Charon is played by Julian Richings.
- Chrysaor – Chrysaor is a half-giant who is the son of Medusa and Poseidon, the brother of Pegasus, and the father of Geryon. He is first mentioned in The Last Olympian when Percy and Annabeth go to see the Oracle of Delphi in the attic of the Big House. A pair of fuzzy dice is said to have been stolen from his car. In The Mark of Athena, Chrysaor and his crew attacked the Argo II in the Mediterranean Sea with the intent to sell Piper and Hazel to Circe, kill Jason, and then give Annabeth and Percy to Gaia. Chrysaor battles Percy on the deck of the Argo II. Once Chrysaor's crew abandon him, Percy surround him. Chrysaor is knocked off the Argo II by Frank and Percy and falls into the sea. A pair of fuzzy dice stolen by a demigod named Gus from Chyrsaor's Honda Civic are found in the Big House attic in The Last Olympia.
- Circe – Circe ran a magical beauty boutique in the Sea of Monsters, where she went by the alias of C.C. While she treated females at her spa, she turned males into guinea pigs. When Percy was turned into a guinea pig, Annabeth used multivitamins from Hermes to restore him, and together they defeated Circe. In The Heroes of Olympus series, it is revealed that Circe employed Reyna and Hylla after they left Puerto Rico and treated them nicely, at least until the pirates were freed and proceeded to capture the sisters.
- Daedalus/Quintus – Architect of the Labyrinth, Daedalus is the son of Athena and the father of Icarus. He killed his nephew Perdix but escaped eternal punishment by casting his soul into automatons. Athena branded him with a murderer's brand in the shape of a partridge. In The Battle of the Labyrinth, Daedalus appears under the alias of a Camp Half-Blood worker named Quintus (meaning "the fifth" in Latin). Percy and Annabeth convince him to use his technical genius to help defeat the Titan army in the Labyrinth. He then accepts death, willing to Annabeth his laptop filled with thousands of years of notes and ideas. In death, he becomes the Underworld's architect and is allowed to visit Icarus and Perdix on weekends.
- Eurytion – Eurytion is a son of Ares who works on Geryon's ranch. He appears in The Battle of the Labyrinth and helps Percy and Annabeth locate Hephaestus.
- Halcyon Green - A son of Apollo gifted with prophecy and under "house arrest" for revealing to a young woman her fate. He gives his life to save Luke Castellan and Thalia Grace in The Diary of Luke Castellan (part of The Demigod Diaries).
- Heracles/Hercules – Heracles is regarded as one of the greatest of Ancient Greek heroes of all time. He is the son of Zeus and Alcmene. Following his death, Zeus brought him up to Mount Olympus to live with him and he was engaged to Hebe. Heracles was mentioned but did not appear in the first book series, usually when monsters that he had fought show up to trouble Percy. In The Titan's Curse, it is revealed that Zoë Nightshade helped Heracles steal the Apples of the Hesperides and gave him a magical sword Riptide which he had forgotten to return, leaving her to be disowned by her sisters and giving her no credit for her help. Hercules appears in The Mark of Athena where he was tasked by Zeus to guard the Pillars of Hercules and issues Piper and Jason a quest for permission to enter the Mediterranean Sea.
- Hyacinthus – Hyacinth was a beloved lover of Apollo. The right for him was contested between Apollo and Zephyrus, and when the former refused to share, Zephyrus caused an accident that led to Apollo's accidental killing over Hyacinthus. His death is regarded by Apollo as one of his two greatest losses of his life, together with Daphne's petrification. Upon his death, Hyacinthus was reincarnated as hyacinth. To this day in The House of Hades, Apollo is still haunted by visions of him.
- Irus – While not strictly a suitor, Irus is a beggar who ran afoul of Odysseus upon his return to Ithica. In The Blood of Olympus, Jason posed as Irus to get close to the ghosts of the Suitors of Penelope.
- King Midas – King Midas was a king who possessed the golden touch which turned anything he touched to gold. He is among the people brought back to life by Gaea in The Lost Hero where his Golden Touch was restored upon him and his son Lityerses emerging from the Doors of Death. It has been mentioned that Midas has occasionally turned Lityerses to gold by mistake causing him to use the nearby lake to wash the gold off him. Jason, Piper, and Leo come to Midas's mansion in Omaha, Nebraska. He was initially polite before revealing his allegiance and turning Leo and Piper into solid gold. Jason fought back against Midas and Lityerses and managed to restore Leo and Piper to life.
- King Minos – King Minos is a former king who becomes one of the judges of the Underworld. Nico consults him in The Battle of the Labyrinth, but Minos kidnaps Nico and tries to kill Daedalus, who constructed the Labyrinth for him. When Daedalus later ends up in the Underworld, Minos unsuccessfully tries to convince the other two judges to punish Daedalus.
- King Sisyphus – A former ruler of Corinth. He had committed violations of guest hospitality, seduced his niece, plotted to kill his brother Salmoneus, and told the River God Asopus where Zeus had his daughter. His major crimes involved cheating death twice. The first where he tricked Thanatos into showing him how the chains worked causing Thanatos to be trapped until Ares freed him (Thanatos being trapped displeased Ares since no one in battle could die). The second time was when he complained to Persephone that his wife Merope did not give him a proper funeral and sent Sisyphus' spirit to the living. Even when Sisyphus did not want to return to the Underworld, he was forcefully dragged back there by Hermes. His punishment in The Fields of Punishment was to push a boulder up a hill. When it got close to the top, the boulder would roll back to the bottom and Sisyphus was condemned to begin again. He appears in The Demigod Files in the story titled The Sword of Hades when Percy and Nico ask him advice while Thalia pushes the boulder up the hill. He does not really help them much, but he does say that he helped someone else. He said that he told that other person to go see Melinoe. Therefore, Percy and his friends go to see Melinoe as Sisyphus begs for them to set him free from his punishment for being here was a minor set-back.
- King Tantalus – Tantalus is the spirit of a king from the Fields of Punishment who is the son of Zeus. He ended up there after killing his son Pelops, cutting him up, and serving him as food to the Gods. His punishment in the Fields of Punishment was to stand under a fruit tree in the middle of a lake. When he tried to pluck the fruit to eat, the branches of the tree rose out of his reach and when he bent down to drink the water, the level would retreat. Tantalus became "tantalised" by having food and drink close to him, but unable to enjoy either. He becomes the activities director at Camp Half-Blood after Chiron is fired. He appears in The Sea of Monsters as a minor character. Even when hired as the activities director, he could not eat or drink as the food kept evading him. Tantalus is shown to hate Percy and his friends even more than he hates most half-bloods, yet shows favoritism to Clarisse, as when naming her hero when the camp was attacked by Colchis Bulls or when she wins the chariot race and throwing a banquet in her honor. When Tyson is brought to camp, Tantalus insults and makes fun of him even when Tyson is claimed by Poseidon. When the camp is attacked by a large flock of Stymphalian birds, Tantalus blames it on Percy, Annabeth, and Tyson's "bad chariot driving" despite that they were the ones who defeated the birds. At the end of the book, his curse is lifted by Dionysus just before he is sent back to the Underworld as he attempts to take some food along. None of the campers are sad to see him go.
- Medea – Medea is a sorceress and a granddaughter of Helios. Jason, Piper, and Leo encounter her in The Lost Hero, where she runs a mall in Chicago. She becomes enraged upon learning Jason's name which he shares her husband, a hero who left her. Her magic causes Jason and Leo to become hostile to one another. Realizing Medea is an agent of Gaea, Piper brings them to their senses and leads their escape before Medea can do anything else to them by blowing up the mall and killing her again.
- Muses - The Muses are the immortal daughters of Zeus and the Titan Mnemosyne. They inspired and presided over several creative arts. In The Lightning Thief, the Muses performed on Mount Olympus at the time when Percy returns Zeus' Master Bolt. As the gods celebrate, the Muses play music that sounds like anything you want, so no one argues about the music. In The Titan's Curse, the Muses perform their music after the Gods decide not to kill Percy and Thalia. According to Percy, everybody hears the music they only want to hear, like classical for the gods and hip hop for the younger demigods. In The Last Olympian, a few Muses are shown playing some tunes on Olympus. Their hearts were not into it because of Kronos' attack on Mount Olympus while the Gods were out fighting Typhon.
- Narcissus – Narcissus was a hunter who was renowned for his beauty and disdained those that had loved him. Nemesis puts a spell on him that causes him to fall in love with the reflection of himself in the water where he dies upon not being able to leave his own reflection. In The Mark of Athena, Narcissus is encountered by Hazel Levesque and Leo Valdez at the Salt Lake in Utah where the demigods are looking for the Celestial Bronze which is needed to help repair the damaged Argo II. When Narcissus realizes that Hazel and Leo have managed to steal his bronze plate which he uses to be able to admire his own reflection, he and a mob of nymphs runs after them trying to kill them.
- Oracle of Delphi – Apollo's Oracle of Delphi resides in the mummified remains of its host, until its power was transferred to Rachel Dare in The Last Olympian. At the end of World War II, the oracle issued the Great Prophecy, saying a child of the Big Three (Zeus, Poseidon, and Hades) would determine the preservation or destruction of Olympus. This caused those gods to form a pact not to father more demigods. In Percy Jackson: Sea of Monsters, the Oracle of Delphi is voiced by Shohreh Aghdashloo.
- Pasiphaë – A Greek sorceress and a daughter of Helios who appears in The House of Hades. She is resentful of the gods for punishing her by giving birth to Minotaur, while her husband, Minos, who caused the problem in the first place, enjoys the right as a judge in the Underworld for being Zeus' son. She is allied with the giants and does a battle of sorcery with Hazel, who manages to trick her into entering an imaginary trapdoor in the Labyrinth.
- Phineus – A blind seer who appears in The Son of Neptune. Percy Jackson finds him in Portland where the Harpies are trying to steal his food. Before he dies from Gaia making him choose a poisoned cup, he reveals to Percy the location of Alcyoneus' camp.
- Procrustes/Crusty – Procrustes is the son of Poseidon who is depicted as a half-giant in this franchise. He is a rogue thief and blacksmith who was previously defeated by Theseus. Procrustes appears in The Lightning Thief as "Crusty," a Los Angeles mattress store owner. He traps Annabeth and Grover on his beds and tries to stretch their spine. Percy defeats him by using Riptide on him.
- Sciron – Scrion is a thief who is the son of Poseidon. He had previously fought Theseus in the past. In The House of Hades, Sciron and his Giant Sea Turtle waylaid the Argo II on the coast of Croatia. Like his fight with Theseus, Hazel defeated Sciron by pushing him off the cliff where he was gobbled by the Giant Sea Turtle.
- Theseus – A hero who is the son of Poseidon and younger than Percy had assumed. When Nico was trying to summon Bianca in The Battle of the Labyrinth, he ended up summoning the spirit of Theseus.
Other Greco-Roman beings
Many of the beings and creatures of Greco-Roman myths are humanoid—in other words, they possess both the intelligence and some of the physical features of humans. The vast majority of these creatures are friendly, such as nymphs and centaurs. Unlike the majority of Greek creatures, these beings are also unquestionably sentient and tend to have larger roles in the novel series.
- Agrius and Oreius – Agrius and Oreius are humanoid bears that were a result of a union between a woman named Polyphonte and a bear due to the power of Aphrodite. They were also the great-grandsons of Ares due to Polyphonte being Ares' granddaughter. The two served as Luke's henchmen in The Sea of Monsters.
- Amazons – The Amazons are a tribe of female warriors who usually worshiped goddesses like Hera and Artemis. Some Amazons appear in The Son of Neptune where they are sent to their compound at Reyna's request. They also run the billion-dollar Amazon.com, which they use as a source of cover and revenue. Though they are often confused with the Hunters of Artemis, the Amazons are not misandrists and like men just fine; they are just a very matriarchal society in which their male spouses are made to work in manual labor while the Amazons work as administrators. In The Blood of Olympus, the Amazons collaborate with the Hunters of Artemis to protect Reyna from Orion, resulting in many casualties.
- Doris – An Amazon who is loyal to Otrera. In The Son of Neptune, she and Lulu guarded Percy Jackson and Frank Zhang.
- Hylla Ramírez-Arellano - Hylla is the older sister of Reyna, the praetor of Camp Jupiter; she is 22 years old. She is a demigod daughter of Bellona and the Amazon Queen. She looks a lot like Reyna with beautiful, glossy black hair and black eyes, long lashes, and a scar on her forehead. She as her sister had the bearing of a swordswoman but stronger. Hylla wears a black suit with a golden belt. Reyna describes her sister as a "chameleon" because she is always changing. They have similar personalities but Hylla seems more funny and "chill". She was born in Puerto Rico and worked for Circe during the first series with her sister. She also spent a year living with pirates and winning the crew's respect. She had an awful childhood, basically she was always trying to protect her sister from their dad. Her father was in the army and the whole Ramírez-Arellano family was favored by Bellona. While worshiping her, Hylla's father falls in love with the idea of war and Bellona. They have the two kids together. Later, the father shows symptoms of PTSD. It turned out he had become a mania, or an insane soul with the worst qualities, and was no longer human. The mania knocks out Hylla, Reyna think she is dead and unknowingly kills her father, who was, technically, already dead. All that was left was the crazed and obsessed remnants of the soul. In "The Blood of Olympus", the Amazon have been working with The Hunters of Artemis who kidnap Reyna and take her to an Amazon headquarters, where Hylla reunites with her sister. Orion breaks into the Amazon HQ and kills every Hunter and Amazon, but the girls escape to their old house, and try to defeat Orion without success. Hylla orders Reyna to leave because she had to stay in combat with the supervivients, hunters, and some Amazons. Though she is never seen afterwards, Orion later confirms that Hylla is still alive after battling him, much to Reyna's relief.
- Kinzie – An Amazon who is the daughter of a nymph and is close and loyal to Hylla. She disarmed Percy and sent Frank flying across the room in "The Son of Neptune." Kinzie also cornered Percy during the Feast of Fortuna and asked Percy out, though he declined. In The Blood of Olympus, Kinzie is killed by Orion.
- Lulu – An Amazon guard who is loyal to Otrera. In The Son of Neptune, Lulu and Doris guarded Percy Jackson and Frank Zhang.
- Otrera – A daughter of Ares and the first Queen of the Amazons who was originally killed by Bellerophon. In The Son of Neptune, she is revealed to be among those who emerged from the Doors of Death. She challenged Hylla for the title of Queen of the Amazons. When she planned to defeat Hylla, Otrera plans to have the Amazons help Gaea and the Giants destroy Camp Jupiter. Hylla manages to defeat Otrera twice until Thanatos is freed from the chains where he was trapped, making sure she would not rise from the dead and challenge her again.
- Arachne – Arachne was once a female weaver who was turned into a spider by Athena after she won in a weaving contest against Arachne. In The Mark of Athena, Arachne appears as a spider-like monster who is the last obstacle for Annabeth's quest to the Athena Parthenos and is in collaboration with Otus and Ephialtes. Annabeth challenges Arachne to a weaving contest where Annabeth tricks Arachne into making monster-sized Chinese handcuffs which Annabeth places onto Arachne. When Annabeth states to Arachne that the Athena Parthenos will restore Mount Olympus, Arachne goes into a fit and brings down her chamber enough to open a chasm to Tartarus. As Arachne falls down into Tartarus, she manages to ensnare Annabeth at the last minute as she and Percy go down the chasm with Nico promising to meet them at the Doors of Death. In The House of Hades, Arachne ambushes Percy and Annabeth which ended with Percy using Riptide to defeat Arachne.
- Antaeus – Antaeus is a half-giant who is the son of Poseidon and Gaea. He was invincible as long as he maintained contact with the ground, so Percy defeated him by hanging him in the air with chains.
- Argus – Argus is a humanoid figure with eyes all over his body who works as a security guard at Camp Half-Blood. He rarely speaks as he is said to have an eye on his tongue. He cares for Hera a lot because she is his mother.
- Cacus – Cacus is a fire-breathing giant. In The Demigod Diaries story titled "Percy Jackson and the Staff of Hermes," Cacus had stolen Hermes' Caduceus. He later attacked Percy Jackson and Annabeth Chase. Annabeth hit Cacus with her metal claw and Percy killed Cacus with Hermes' Caduceus.
- Centaur – Centaurs are half-man, half-horse creatures, often depicted as wild and drunk. Chiron is the only truly civilized centaur. Many of his kin are part of the Party Ponies. There are other centaurs who work for Gaea's army.
- Chiron – Chiron is a centaur with a white stallion body and a son of Kronos. He is the mentor of Percy Jackson and the activities director at Camp Half-Blood. In The Lightning Thief, he first appears, disguised as a Latin teacher at Percy's school. He uses an enchanted wheelchair to conceal his horse half. Chiron is played by Pierce Brosnan in the first film and by Anthony Head in the second film.
- Horned Centaurs - A race of centaurs with horns sticking out of their heads and their horse half is palomino. These centaurs enjoy killing demigods. In The Son of Neptune, they attacked Camp Jupiter where most of them were either killed or have retreated.
- Party Ponies – They are Chiron's kin. As their name suggests, they are a vast clan-like extended family of rowdy centaurs who reside in the United States with chapters hailing from each respective state. They are key players in two major incidents in the series. In The Sea of Monsters, they go along with Chiron and rescue Percy from Luke during their duel on the Princess Andromeda. In The Last Olympian, they help Chiron and the others fight the major battle between the gods and the Titans.
- Larry – Member of the Party Ponies.
- Owen – Member of the Party Ponies.
- Cyclops – A race of one-eyed giants who have four species as mentioned in "The Lost Hero". The first group of Cyclopes are the Elder Cyclops who are the sons of Gaea and Ouranos where they alongside the Hecatonchires were imprisoned in Tartarus by Ouranos. They are friendly and help the gods ever since the Titanomachy when they were freed from their imprisonment. The second group of Cyclopes are the ones who are the children of Poseidon. Tyson is one of these. The third group of Cyclopes is the southern group who raise goats and live in caves. The fourth group of Cyclopes is the northern group who helped the Titans make weapons and are smarter than the southern group of Cyclopes. Some northern Cyclopes were seen fighting with Kronos' army in "The Battle of Manhattan."
- Ma Gasket – A 12 ft. female cyclops of the Northern Cyclops faction who is the mother of Sump and Torque. She appears in "The Lost Hero" when Jason, Piper, and Leo visit her factory. In "The Son of Neptune," Ma Gasket leads the Cyclopes in an attack on Camp Jupiter where she is defeated by Tyson.
- Sump – The son of Ma Gasket who appears in "The Lost Hero".
- Torque – The son of Ma Gasket who appears in "The Lost Hero."
- Polyphemus – A 15 ft. cyclops of the Southern Faction. Percy Jackson and his friends encounter him on an island in "The Sea of Monsters." He is shown to be blind and there was also a reference about Odysseus being responsible for blinding him under the alias of "Nobody". When Polyphemus tries to pray to Poseidon to get revenge on Percy for hurting him, Percy states that Poseidon is also his father. He later tried to eat them only for them to escape. In Percy Jackson: Sea of Monsters, Polyphemus is portrayed by Robert Maillet and voiced by Ron Perlman.
- Ma Gasket – A 12 ft. female cyclops of the Northern Cyclops faction who is the mother of Sump and Torque. She appears in "The Lost Hero" when Jason, Piper, and Leo visit her factory. In "The Son of Neptune," Ma Gasket leads the Cyclopes in an attack on Camp Jupiter where she is defeated by Tyson.
- Echidna – Part woman, part snake. She is the wife of Typhon and the mother of Cerberus, Chimera, Hydra, the Nemean Lion, and Ladon as well as several others not in the series. She is first seen as an old lady who owned a chihuahua which was actually Chimera in disguise. Echidna also detests that there is a marsupial that was named after her. She assisted Chimera in fighting Percy at the top of the St. Louis Arch. She and Chimera disappeared after Percy dove into the water.
- Empousai – Seductive shape-shifting women who are similar in appearance to vampires, but have one shaggy donkey leg and one bronze leg. Two Empusa pose as cheerleaders in "The Battle of the Labyrinth." In The Last Olympian, an unnamed Empousai appears as part of the truce party along with Prometheus, Morrain, and Ethan Nakumura. She stated that she was among the things that was released from Pandora's pithos (Pandora's Box).
- Kelli – An Empousai that poses as a cheerleader in "The Battle of the Labyrinth." She was killed by Annabeth. In "The House of Hades," Kelli is among the Empousai that make their way to the Doors of Death so that Kelli can get even with Percy. With the help of Bob the Titan, Percy and Annabeth defeat Kelli and the Empousai.
- Seraphone – An Empousai who distrusts Kelli and fears Hecate. In "The House of Hades," Seraphone is among the Empousai that make their way to the Doors of Death. When they attack Percy and Annabeth, Annabeth tricks the Empousai into believing that Kelli was useless and weak and that she was leading them all into danger. Annabeth tells them to follow Serephone as she was older and wiser. Hearing this made Serephone happy and declared that she was a leader. Kelli became angry and killed Serephone.
- Tammi – An Empousai that poses as a cheerleader in "The Battle of the Labyrinth." She was killed by Percy Jackson.
- The Fates – The three women who are the personification of destiny and are controllers of the threads of life. In The Lightning Thief, Percy and Grover encounter them at an old-fashioned fruit stand. In The Last Olympian, the Fates take Luke's dead body away after the Second Olympian War. In The Blood of Olympus, the Fates are seen fighting their old enemy Thoon and killing him the same way they did back in the Gigantomachy.
- Faun – The fauns are Roman counterparts of satyrs. In contrast to Camp Half-Blood's helpful satyrs, the fauns are mostly beggars and are often used for amusement purposes.
- Don – One of the Fauns that live at Camp Jupiter. In "The Son of Neptune," Percy and Hazel run into Don who needs money for making up bad lies. When Percy asks why the Fauns aren't like the Satyrs, Don states that Fauns are free-spirited.
- The Furies – The Furies are Hades' chief servants and torturers and they personally searched for Hades's Helm of Darkness, believing that Percy had stolen it.
- Alecto – Alecto acted as Percy's pre-algebra teacher Mrs. Dodds in the first book. She is Hades's main servant. In The Last Olympian, Alecto acted as the lawyer who rescued Nico and Bianca di Angelo from the Lotus hotel. In the film adaption, Alecto is portrayed by Maria Olsen.
- Megaera – A Fury representing grudging.
- Tisiphone – A Fury representing avenged murder.
- Geryon – In this series, Geryon is described as having a normal head, a face weathered and brown from years in the sun, slick black hair, a pencil-thin moustache, two very beefy legs wearing a very large pair of Levis and 3 chests wearing a different colored shirt: green, yellow and red. In "The Battle of the Labyrinth," he is the owner of Triple G Ranch with Orthrus guarding the ranch. He gave Percy an apparently impossible task; cleaning out the stables of carnivorous horses, one of the Labors of Hercules. Percy managed to complete the task, but Geryon went back on his deal to let Percy's friends free and the two fought. Percy found Geryon a strong opponent, as Geryon's three hearts made him almost impossible to defeat. Percy defeated Geryon with a well placed arrow (thanks to Hera) that went through Geryon's side hitting all three hearts at once, killing Geryon. In The House of Hades, Geryon had cursed Percy to feel the pain he had when Percy killed him. The Arai later told Percy about this. Percy later spotted Geryon among the characters awaiting their turn to go through the Doors of Death.
- Ghoul – The Ghouls serve as security guards in the Underworld and make a sound that is similar to bats. They escort the souls of the wicked to the Fields of Punishment as seen in "The Lightning Thief" when they take a preacher who had been scamming people there.
- Giant - The Giants are a race of humanoid monsters of great stature and strength. Besides the Cyclopes and the Gigantes, there are different species of giants in Greek mythology.
- Gegeines – A race of 7 ft. to 8 ft. six-armed giants in leather loincloths who previously fought Jason and the Argonauts. They appear in The Lost Hero where they are summoned by Enceladus to fight Jason, Piper, and Leo.
- Hekatonkheires – The Hundred-Handed Giants of incredible strength, superior even to the Cyclopes. They are taller than mountains and their arms are as thin as noodles. Like the Elder Cyclopes, the Hekatonkheires are the children of Gaea and Ouranos where they were hurled into Tartaus by Uranus. The Hekatonkheires and the Elder Cyclopes were later freed by Zeus where they helped him in the Titanomachy. In the film Percy Jackson: Sea of Monsters, a Hekatonkheires (portrayed by Anthony Shim) worked as a barista at a coffee shop with a harpy. Its appearance in the film was depicted as having eight arms when in the presence of demigods.
- Briares – Briares is a Hekatonkheires. Briares was imprisoned on Alcatraz Island by Kampê in the fourth book. It is mentioned that his brothers Cottus and Gyges have faded because people have forgotten about them. When Tyson finds that Briares (his hero) is too afraid to escape, he is heartbroken. At the end, Briares returns to help defeat Luke and the Titans. In The Last Olympian, Percy sees Briares helping Poseidon defeat the forces of Oceanus.
- Hyperborean – The Hyperboreans are a race of 30 ft. Snow Giants with blue skin ice-gray hair that come from Hyperborea. When wounded, the Hyperborean will bleed blue blood. They can freeze object and people using their frosty breath. When defeated, the Hyperborean freeze into ice. In The Last Olympian, the Hyperboreans are on the side of the Titans. In The Son of Neptune, a group of peaceful Hyperboreans were seen in Anchorage, Alaska.
- Morrain – A Hyperborean who appeared in The Last Olympian. He was a part of a truce meeting. He wasn't seen taking part in the Battle of Manhattan and his current fate is unknown.
- Laistrygonian – The Laistrygonians are a race of 8 ft. muscular cannibal giants who were previously encountered by Odysseus. In "The Sea of Monsters," three Laistrygonians serve as the brawn of Kronos's army as seen in "The Sea of Monsters." Three of them infiltrated Percy's school as visitors from Detroit and attacked the students with flaming dodgeballs. They were defeated by Percy, Annabeth, and Tyson. In "The Battle of the Labyrinth," a Laistrygonian assisted Kelli the Empousai into capturing Percy, Annabeth, and Rachael where they were marched to Antaeus' lair. Two more Laistrygonians were seen in Daedalus' lair where they followed Minos and carrying Nico with them. When the Titan army made their way through the Labyrinth and attacked Camp Half-Blood, the Laistrygonians were among the monsters that took part in the attack. They were pushed back by the campers in Apollo's cabin and the Laistrygonians retreated when Grover unleashed the powers of Pan. In "The Last Olympian," The Laistrygonians were seen in The Battle of the Labyrinth. When one Laistrygonian tried to attack Sally Jackson, she managed to shoot it.
- Joe Bob – A Laistrygonian.
- Marrow Sucker – A Laistrygonian.
- Skull Eater – A Laistrygonian.
- Gorgon – A Gorgon is a female humanoid creature with snakes for hair. Anyone who looks at the face of the Gorgon Medusa turns to stone.
- Medusa – The Gorgon who is the sister of Stheno and Euryale. Under the moniker of "Aunty Em," she attempted to lure Percy, Annabeth, and Grover into a false sense of security and turn them into stone statues. She is defeated and her severed head is mailed to the gods of Olympus as proof of the trio's courage (though Grover notes that it is more akin to impertinence). Percy's mom previously uses her head to turn Gabe Ugliano to stone. In the film adaptation, Medusa is portrayed by Uma Thurman.
- Stheno – A Gorgon who is the sister of Medusa and Euryale. In "The Lost Hero," she was mentioned to be among the characters who were brought back to life when the Doors of Death opened. Stheno is later found to be chasing Percy (with her sister Euryale) and is described by Percy as appearing as a dumpy old grandmother but with rooster feet and bronze boar tusk sticking out of the corners of her mouth.
- Euryale – A Gorgon who is the sister of Medusa and Stheno.
- Gray Sisters – The Gray Sisters are women who share one eye and one tooth. In "The Sea of Monsters," Percy, Annabeth, and Tyson run into the Gray Sisters who are in the form of three taxi drivers. During the Gray Sisters' argument, Percy manages to grab their eye and demand the location of which they had mentioned. They tell him 30, 31, 75, 12 which Percy didn't understand. He however gave the eye to Wasp and they drop the three off at Camp Half-Blood. Later at the campfire, Percy figures out that the numbers were used for longitude and latitude which leads to the Sea of Monsters. In the film adaptation, the Gray Sisters are portrayed by Mary Birdsong, Yvette Nicole Brown, and Missi Pyle.
- Harpy – Harpies are winged spirits of sudden, sharp gusts of wind. They were known as the "Hounds of Zeus" and were dispatched by the god to snatch away (harpazô) people and things from the Earth. Sudden, mysterious disappearances were often attributed to the Harpies. There are three Harpies that were created by Zeus. They work in Camp Half-Blood as "the Cleaning Harpies" being allowed to eat any camper who stays in Camp Half-Blood past noon in the last day of the summer without completing their form or if the camper is caught sneaking out of their cabin at night. Percy Jackson refers to the "Cleaning Harpies" as if they were "crossbred with the dodo birds." The Harpies also cleaned the dishes with super-hot lava and are also good in mid-town traffic. In "The Titan's Curse," it is shown that there are some Harpies that are on the side of the Titans. In the film Percy Jackson: Sea of Monsters, a harpy (portrayed by Camille Atebe) worked as a barista at a coffee shop with a Hekatonkheires.
- Aello – A Harpy whose name means "storm swift." She is a member of Camp Half-Blood's "Cleaning Harpies."
- Celaeno – A Harpy whose name means "the dark." She is a member of Camp Half-Blood's "Cleaning Harpies." Celaeno is also known as Podarge (which means "fleet-foot").
- Ella – Ella is a Harpy who appears in The Son of Neptune. She has red hair and feathers, grey eyes, and a bony structure. She has extensive knowledge about the Romans and their culture. Ella is very valuable to the enemy side as she might have knowledge of several scrolls of prophecies. She has memorized a lot of books, and often recites a few prophecies from the Sybilline books that Octavian desperately wants. It is mentioned towards the end of The Son of Neptune, that Ella needed to be hidden from Octavian because of this important knowledge. She was one of the Harpies who was trying to torment the blind psychic Phineas. Near the end of the book, it is revealed that Tyson has a crush on Ella and that she has a crush on Tyson. Because of this, Ella remains with Tyson at Camp Jupiter.
- Ocypete – A Harpy whose name means "the swift wing." She is a member of Camp Half-Blood's "Cleaning Harpies."
- Hunters of Artemis – The Hunters of Artemis are a group of immortal virgin girls who gave up love in exchange for immortality and youthfulness. As their name implies, they are followers of Artemis in her hunts, though a lieutenant in chosen to lead them when Artemis is not around. Members are recruited both from mortals and demigods. They have a strong aversion to males and tend to regard them as disgusting and untrustworthy. However, their immortality will fade if they ever fall in love or "fall in battle". In battles, the hunters primarily use bows to attack. Zoë Nightshade serves as the group's lieutenant for over 2000 years, but after her death in The Titan's Curse, she is succeeded by Thalia Grace. In The Blood of Olympus, many members are massacred by the Gigante Orion (who is not the mythical Orion that Artemis knew) while attempting to give Reyna time to escape from Puerto Rico.
- Celyn – Celyn is a hunter who appears in The Blood of Olympus. She is killed by Orion.
- Naomi – Naomi is a daughter of Hecate and another hunter who captures Reyna in The Blood of Olympus. She is killed by Orion.
- Phoebe – Phoebe is one of the Hunters of Artemis, the best tracker among them. She is suspicious of boys. She appears in The Titan's Curse, The Lost Hero and The Blood of Olympus. In The Blood of Olympus, she is revealed to have looked about 14 and to have lived since Artemis first knew Orion. She eventually dies by the hands of Orion.
- Zoë Nightshade – Zoë was the leader of the Hunters of Artemis. She appears in The Titan's Curse. She was a daughter of Atlas and the sea goddess Pleione. She crafted Riptide (Percy's magic sword), but lost it to Hercules. She was once one of the Hesperides, but she was disowned by her family for helping Hercules. In The Titan's Curse, she is killed by Atlas. In remembrance of her sacrifice, Artemis turns her into a constellation called "The Huntress."
- Ichthyocentaur – The Ichthyocentaurs are creatures that have the upper bodies of men, the lower fore-parts of horses, ending in the serpentine tails of fish. Their brows were adorned with a pair of lobster-claw horns. In The Mark of Athena, the demigods encounter the Ichthyocentaurs who save them from Keto and her children. The Icthyocentaurs also run a Camp for Merpeople heroes.
- Aphros – An Ichthyocentaur who is the half-brother of Chiron. He teaches home economics.
- Bythos – An Ichthyocentaur who is the half-brother of Chiron. He teaches fighting.
- Kampê – A snake-haired winged centauroid creature who is half-woman, half-dragon with the heads of various mutated wild animals growing from her human torso. She is a monster who imprisoned the Hundred-Handed Ones and Cyclopes during the First Great War. She is feared by all, and is defeated by Briares in the "Battle of the Labyrinth" by being crushed by boulders.
- Kerkopes – Passalos and Akmon are two brothers who are the children of Oceanus and Theia. They worked as thieves until they were caught by Hercules and later turned into monkeys by Zeus. In The House of Hades, the Kerkopes have set up shop in Balogna, Italy. When the Argo II docks there, the Kerkopes attacked the ship and robbed it, taking things like an Archimedes Sphere and Piper McLean's dagger Katoptris. Leo Valdez and Jason At the Fountain of Neptune, they incapacitated Jason by trapping him in a net. Leo chases them to their hide-out and defeats them with a home-made flash-bang grenade. He then got their possessions back and agreed not to kill Passalos and Akmon on the condition that they go to America and disrupt the Romans in order to slow down their attack on Camp Half-Blood. Later in a dream, it is shown that they are being very successful in this goal.
- Lamia – Lamia is the daughter of Hecate who was one of the former love interests of Zeus until Hera turned her into a monster after the death of her children. In "The Demigod Diaries" story titled "Son of Magic," Lamia is revived by Gaia to kill Hecate's son Alabaster Torrington. Alabaster manages to defeat Lamia until Hecate arrives to save both her children. According to Hecate, Lamia won't try attacking Alabaster again, knowing he could use that spell against her.
- Lotus-eaters – A number of them run the Lotus Hotel and Casino in The Lightning Thief. The hotel is filled with arcade games that makes visitors not want to leave. They are also mentioned in the Odyssey by Homer.
- Maenad – A bunch of Maenads appeared in The Demigod Diaries story "Leo Valdez and the Quest for Buford." They were seen skipping in a mall-shaped clearing in the Camp Half-Blood Forest where a Drakon appeared. They managed to easily rip it apart with their long white talons and their elongated wolf-like fangs.
- Manticore – The Manticore is a monst that has the face of a man, the body of a lion, and the tail of a scorpion. In Percy Jackson: Sea of Monsters, a Manticore (played by Daniel Cudmore) appeared as a top henchman of Luke Castellan. When it came to the fight at Polyphemus' lair, the Manticore wounded Annabeth before it was killed by Grover Underwood and Clarissa La Rue.
- Dr. Thorn – A Manticore in human form that appeared in The Titan's Curse. Dr. Thorn is the vice-principal of Westover Hall (the school that Bianca and Nico di Angelo attended). He has two eyes of different colours, one blue and one brown. His nostrils flare up when he talks. He speaks in a French accent. He tries to kill people by using thorn-like objects. He is angry that in the ancient days, the Gods forced him to live out in Persia, where he never had any decent challenges, as he would in Ancient Greece. He is killed by Dionysus.
- Merpeople – A race of sea creatures that are half-human and half-fish. The male merpeople are called Mermen while the female merpeople are called Mermaids. In "The Last Olympian," Percy wakes up underwater near Atlantis where he sees various Merpeople in battle armor fighting the forces of Oceanus. There were even some Merpeople making graves for the Merpeople who fell in battle. They serve Poseidon.
- Bill – A merman that was trained at "Camp Fish-Blood" (as Leo called it) by Aphros and Bythos.
- Minotaur – The Minotaur is part-man, part bull. The monster of the labyrinth who chased Percy all the way to Camp Half-Blood. Percy defeats the monster atop Half-Blood hill and claims its broken horn as a spoil of war. The Minotaur returns in The Last Olympian as a general for Kronos's army at Williamsburg Bridge and now wearing armor. It was defeated by Percy again. In the film adaptation, the Minotaur's head resembles a Cape Buffalo's head.
- Nymphs - female, magical beings usually associated with some natural feature. Many different kinds of nymphs are seen in Rick Riordan's novels, including naiads (river nymphs), dryads (tree nymphs), and aurae (wind nymphs).
- Aurae – The Aurae are wind spirits who work at Camp Jupiter as seen in The Son of Neptune.
- Mellie – An Aurae. She is the personal assistant of Aeolus as seen in "The Lost Hero." At the end of The Lost Hero she works as Piper's dad's assistant, Tristan McLean.
- Dryad – Dryads are a species of nymphs that are associated with trees and forests.
- Daphne – Daphne is a dryad whom Apollo fell in love with. Eros, after a conflict with Apollo, shot an arrow that made the latter fall in love with Daphne, yet at the same time shot an arrow that made Daphne hate him. She ran away and, realizing that Apollo would never give up, asked Gaea to transform her into a tree. Apollo still grieves for Daphne's fate, which he considered as one of his two greatest losses, and is frequently haunted by visions of her and other dryads blaming him.
- Juniper – Juniper is Grover Underwood's girlfriend. In The Battle of the Labyrinth, she informs Percy that she has seen Luke Castellan using the entrance to the Labyrinth and that she has also seen Quintus/Daedalus using the entrance to the Labyrinth.
- The Hesperides – The Hesperides are the three daughters of the Titan Atlas and the sea goddess Pleione who tend to the Garden of the Hesperides which is accessible only during sunset. They are described as looking identical to their estranged sister Zoë Nightshade who was originally a part of them before she became disowned for supporting the gods during the Titan War. They briefly reunite with Zoë and then accompanying Percy and the others in heading to Mount Tamalpais in The Titan's Curse. They warned them that they will not be a match against Atlas and pulled the Ladon card. Zoë retaliates by waking Ladon with a shout, and calling her sisters cowards when they chided her for insanity. As Zoë distracted Ladon to help Percy and Thalia evade it, the oldest of the Hesperides called Zoë a fool and they disappeared.
- Oreads - The Oreads are a race of mountain nymphs.
- Echo – An Oread who loved her voice. Zeus fell in love with Echo causing Hera to curse Echo into repeating everything she says. She did have an encounter with Narcissus at the time when he was admiring his reflection in the water. When Echo evaded the love advances of Pan, she was killed by some panicked shepherds and her fragments were scattered by Gaea. In The Mark of Athena, Leo Valdez and Hazel Levesque encounter Echo on a small island where they were looking for lime and Celestial Bronze that was needed to repair the damaged Argo II. Echo helps Leo get the Celestial Bronze from the lake as Leo makes insults towards Narcissus which Echo repeats. Before Leo leaves, Echo kisses him and briefly becomes more visible; Leo describes her as beautiful, but forgettable
- Naiads – The Naiads are nature spirits that inhabit streams and rivers and lakes, or any fresh body of water.
- Brooke – Naiad that inhabits the brook in Camp Half-Blood. Gave a warning to Leo, Piper and Jason about her "Crazy Cousins" in The Quest for Buford.
- Cloud Nymphs - The Cloud Nymphs are mentioned briefly in the series, particularly in The Heroes of Olympus.
- Fleecy – Fleecy is a cloud nymph who works at Iris's co-op. She appears in The Son of Neptune. She manages Iris-messaging after Iris begins focusing on her shop. Fleecy is described as young, with frizzy white hair and eyes that change colors from gray to white to black.
- Aurae – The Aurae are wind spirits who work at Camp Jupiter as seen in The Son of Neptune.
- Palikoi – Geyser gods who in times past were worshiped by runaway slaves for protection. Others can make oaths with them. While oaths toward Styx are prolonged and cancerous, a single breach of oath with the Palikoi will result in immediate death.
- Pete – A Palikoi employed by a marketing company. He is tasked to operate in the Woods of the Camp Half-Blood while collecting surveys on customer service. Apollo makes an oath with Pete to rescue Meg who is kidnapped by the Myrmekes.
- Paulie – Pete's fellow worker in a marketing company. He is kidnapped by Nero who intends to use his power to break through the Grove of Dodona's walls. Apollo is able to rescue him along with the other abducted demigods.
- Satyr – Half man, half goat. Most of the Satyrs work at Camp Half-Blood. Their Roman counterpart are the Fauns. Grover Underwood is a satyr.
- Council of Cloven Elders – A group of Satyrs whose main duty is to abide over the Satyrs' search for Pan. The Council of Cloven Elders reside in the forum within Camp Half-Blood's forest are responsible for determining which Satyrs are worthy of receiving a searchers' license. To achieve a searcher's license, a Satyr must be a successful protector where they must bring a Demigod to Camp Half-Blood alive.
- Leneus – Leneus is a member of the Council of Cloven Elders who hates Grover and thinks he is a liar. He is killed in The Last Olympian and is reincarnated as a laurel. When he dies, Grover takes his place in the Council of Cloven Elders.
- Maron – Maron is a member of the Council of Cloven Elders. He only appears in book four, when he, Silenus and Leneus try to exile Grover because they think that Pan, the god of the wild, is still alive and Grover is lying about his death. He and the other members of the Council are described as being old and fat satyrs.
- Silenus – Silenus appears in books four and five. He is the leader of the Council of Cloven Elders and is shown to hate Grover calling him an "outcast" and a "liar." He also has suspicions that Grover is a spy.
- Ichneutae – Ichneutae is a satyr who is exclusive to the film Percy Jackson: Sea of Monsters portrayed by Jordan Weller. Ichneutae was present when Clarisse won the obstacle tower. He was chosen by Dionysus to guide her to the Golden Fleece. Clarisse mentioned that he was eaten by Scylla and his last words were "I got this."
- Lysas – Lysas was a satyr who was mentioned to have been the chosen one of Pan where he was tasked by the god himself to spread the word that "The great god Pan has died." Even though he refused to believe this, he spread the word to the world in Ephesos. In "The Lightning Thief," Grover Underwood mentions that a sailor off the coast of Ephesos heard a mysterious cry saying that Pan has died. It is revealed in "The Battle of the Labyrinth" that it was a satyr called Lysas.
- Millard and Herbert – Millard and Herbert are two satyrs sent by Chiron to find and alert Rachel Dare to visit Camp Half-Blood in The Hidden Oracle. While Rachel is successfully courted in, she states that the satyrs came to her wounded and died soon afterward.
- Uncle Ferdinand – Ferdinand is Grover's uncle who was one of the victims of Medusa in the Garden Gnome Emporium. When Kronos' army was hiding out there in "The Last Olympian," his statue form is now missing an arm and has graffiti on it without Medusa to watch over it.
- Woodrow – Woodrow is Camp Half-Blood's music instructor. He is afraid of Apollo due to the latter's apparent history of flaying a satyr due to his loss in a musical contest, which Apollo himself vehemently denies.
- Council of Cloven Elders – A group of Satyrs whose main duty is to abide over the Satyrs' search for Pan. The Council of Cloven Elders reside in the forum within Camp Half-Blood's forest are responsible for determining which Satyrs are worthy of receiving a searchers' license. To achieve a searcher's license, a Satyr must be a successful protector where they must bring a Demigod to Camp Half-Blood alive.
- Scythian Dracaenae – A race of humanoid females with twin snake tails in place of legs. They make up a considerable portion of the Titan Lord's forces. In "The Sea of Monsters," Percy first encounters them on the Princess Andromeda. In "The Titan's Curse," some Scythian Dracaenae attacked Percy's group after he had defeated Atlas. In "The Battle of the Labyrinth," Percy fights a Scythian Dracaenae in Antaeus' lair. Percy almost immediately kills it much to Antaeus' disapproval. The Scythian Dracaenae also show up in the actual Battle of the Labyrinth as one of the main types of soldiers. In "The Last Olympian," the Scythian Dracaenae are seen taking part in the Titan Army's attack on Manhattan.
- Queen Sess – The Queen of the Scythian Dracaenae who appears in "The Last Olympian." She fought Chiron alongside Kronos and was killed when Chiron fired one of his arrows in between Queen Sess' eyes.
- Suitors of Penelope – The Suitors of Penelope were men who competed to become the next wife to Penelope when they believed that she became a widow when Odysseus was fighting in the Trojan War. When Odysseus returned, his disguised appearance spoke to Penelope to hold a contest where the Suitor that can string Odysseus' bow will become her new wife. When Odysseus won the contest, he sheds his disguise and kills the Suitors with the help of Telemachus and Philoeteus. In The Blood of Olympus, Jason, Piper, and Annabeth encounter the ghosts of the Suitors of Penelope on Ithica where they are now allied with Gaea.
- Werewolf – A werewolf is a creature that is part man, part wolf. In The Lost Hero, King Lycaon led a pack of werewolves to kill Valdez and McLean. Most of the werewolves were defeated by the Hunters of Artemis.
- King Lycaon – Lycaon was a king who was turned into a wolf after attempting to test Zeus's omniscience. In The Lost Hero, Lycaon encounters Jason, Leo, and Piper in their search for Aeolus. He and his werewolves attempt to kidnap Jason and kill Leo and Piper at Gaia's command. The Hunters of Artemis thwart the plan, but Lycaon escapes. In The Blood of Olympus, Lycaon confronts Reyna, Nico, and Coach Hedge at Évora to prevent them from delivering the Athena Parthenos to Camp Half-Blood, but he is stabbed by Reyna's silver knife.
- Zombie – A bunch of Zombies were seen as passengers on the Princess Andromeda in The Sea of Monsters. Clarisse used the zombies of Confederate soldiers to operate the CSS Birmingham.
- Apollo's Cattle – The sacred cattle herd of Apollo. In The Battle of the Labyrinth, Apollo's Cattle were seen at the Triple G Ranch under Geryon's care since Apollo never has time to take care of them. Apollo was unaware that he was using some of the cattle for meat and feeding them to the monsters that work for Kronos. Although Apollo didn't have any cattle in actual Greek mythology, these cattle are based on the Cattle of Helios.
- Arai – The Arai is a race of winged female daemons who inhabit Tartarus. They are similar to the Furies, but their number is not limited to three, and they are under control of their mother, Nyx, instead of Hades. The spirits carry the grudge of anyone whom their killer have wronged; when Percy kills some of them, they release the grudges of Kampê's death by crushing and Calypso's isolation in Ogygia.
- Arion – Arion is a horse born to Neptune and Ceres, making him Percy's half-brother. He appears in The Son of Neptune where Hazel frees him from the Amazons. He is described as having a tan coat with a black mane and tail. He is a free spirit and seems to have a bad temper, being known to curse when his abilities are challenged.
- Automaton – Automatons are similar to highly developed robots with intricate circuitry that makes them hard to fix. Most are made out of steel, but some like Festus the dragon are made out of celestial bronze or other materials. In the Percy Jackson & the Olympians series, Annabeth discovers that many statues in Manhattan are actually automatons created by Daedalus, an army that could either defend or attack Olympus.
- Argentium – Reyna's silver Automaton Hound who appears in The Son of Neptune, The Mark of Athena and The House of Hades.
- Aurum – Reyna's gold Automaton Hound who appears in The Son of Neptune, The Mark of Athena and The House of Hades.
- Bronze Dragon – An automaton dragon made of bronze created by the campers in Hephaestus' cabin to help defend Camp Half-Blood. He is first shown in "Percy Jackson and the Bronze Dragon" story of "The Demigod Files" where Percy, Annabeth, and Silena reactivate it in order to save Charles Beckendorf from the Myrmekes. He was deactivated by Beckendorf with Percy's help afterwards, due to the fact that it was unstable and dangerous. It is fixed by the Hephaestus cabin to protect the camp sometime after this. He is later named "Festus" by Leo Valdez in "The Lost Hero" when Leo found him hidden in the forest. Leo manages to forge some wings onto Festus. Although Festus was sliced to bits by the lasers on King Midas' mansion, Festus' head was recovered by Hephaestus who had his cabin build the Argo II with Festus' head as the ship's figurehead. Festus means "happy" in Latin.
- Celedon - The Celedons are automatons forged by Hephaestus to serve as Apollo's backup singers. In Percy Jackson and the Singer of Apollo, Percy Jackson had to find the fourth Celedon for Apollo after it left Mount Olympus and fled into Times Square.
- Colossus of Nero – The Colossus of Nero is a gigantic automaton built under Nero's orders in the images of Apollo and himself. Nero uses the statue to invade Camp Half-Blood in The Hidden Oracle. The Colossus proceeds to destroy the Dining Area and Demeter's Cabin before being infected with Apollo's hay fever plague and subsequently decapitated.
- Mechanical Spiders - A bunch of automaton spiders that were created by Hephaestus.
- Talos – Talos is a giant automaton. Percy, Thalia, and Bianca fight a prototype of Talos in the Junkyard of the Gods. Apparently, he has a manhole at the base of his foot for 'servicing'. Bianca went in to mess up his circuit so they could defeat him. He fell on some power lines thus electrocuting Bianca.
- Basilisk – Basilisks are small green snakes with colorful spikes and poisonous bites and they can breathe fire. In The Son of Neptune, they attacked Camp Jupiter, but Frank shapeshifts into a mongoose (or weasel) and scares them off.
- Buford - Buford is a walking table that Leo Valdez saved from a supply closet and prefers to be polished by Lemon Pledge instead of Windex. He assists Leo Valdez in constructing the Argo II in Bunker 9. Eventually, Leo programs a talking mini-hologram of Gleeson Hedge onto Buford.
- Cerberus – The three-headed dog who guards the entrance to the Underworld. In The Lightning Thief, he befriends Annabeth. He also appears in The Last Olympian when he is playing with Mrs. O'Leary. Cereberus is the son of Echidna and Typhon.
- Charybdis – One of the two monsters (the other being Scylla) who live on either side of a narrow channel of water (the entrance to the Sea of Monsters). She takes the form of a giant mouth that swallows and releases water, creating whirlpools. she is described by Percy as an "orthodontist's nightmare".
- Chimera – A three-headed beast that is part lion, part goat, and has a snake-headed tail. It is first seen in the form of a Chihuahua. It confronted Percy atop the St. Louis Arch alongside its mother, Echidna. Overwhelmed by the creature and poisoned by its snake head, Percy was forced to jump into the water far below to escape it. It disappeared after Percy dove into the water.
- Clazmonian Sow – A flying pig that appeared directly after Hyperion was defeated. Percy defeats it with the help of Blackjack, a statue of Hermes, and the New York Public Library's two stone lion statues (that were really automatons).
- Colchis Bull – The Colchis Bulls are elephant-sized, fire-breathing bronze bulls created by Hephaestus with horns of silver and rubies for eyes. In The Sea of Monsters, some of these bulls attack Camp Half-Blood and are defeated by Tyson. They were later used to make the tracks for the Chariot Race.
- Dragons - Dragons are large reptilian creatures that sometimes have wings. They are used for guarding things and are younger than Drakons.
- Draco Aionius – Some of these monsters attacked Camp Half-Blood while Percy Jackson was on his adventures in the "The Sea of Monsters".
- Ladon – Ladon is a giant dragon who is one of the offspring of Echidna. It defends the Hesperides' apple tree. Ladon poisons Zoë Nightshade in The Titan's Curse.
- Peleus – A dragon that is now guarding the Golden Fleece which hangs on the tree that Thalia was previously within. He is possibly named after Peleus: Father of Achilles.
- Python - A giant Earth Dragon who was an old enemy of Apollo. In The Blood of Olympus, Python was revived by Gaea during the Second Gigantomachy and it was mentioned that Python reclaiming Delphi was one of Apollo's many failures. In The Hidden Oracle, Apollo and Meg McCaffrey are in the Labyrinth where they overhear Python talking to Nero about the plans to control all the Oracles.
- Drakons – A race of giant serpent-like creatures that are several millennia older than dragons. They come in three different types: Aethiopian, Lydian, and Maeonian. In The Demigod Diaries story titled "Leo Valdez and the Quest for Buford," an unidentified Drakon appeared in the Camp Half-Blood Forest until it was ripped apart by the Maenads.
- Aethiopian Drakon – A Drakon with terrifying green eyes that originated from Africa. One was being raised by Luke in The Sea of Monsters. When one of the Bear Twins seemed reluctant to do his bidding, Luke threatened to feed him to the Drakon. In The Battle of the Labyrinth, an Aethiopian Drakon was seen in the cargo bay of the Princess Andromeda.
- Lydian Drakon – The oldest and fiercest of the Drakons that once attacked the village of Lydia. It is a 200 ft. long Drakon with a paralyzing stare in sheer terror and armor-corroding acidic venom. In The Last Olympian, Kronos unleashed it upon Manhattan where it killed many half-bloods before being killed by Clarisse La Rue.
- Maeonian Drakon – A green and yellow Drakon that once attacked Maenoia, Turkey. In The House of Hades, the Maeonian Drakon resides in the swamps of Tartarus. It attacked Percy, Annabeth, and Bob the Titan and was killed by Damasen. Damasen's curse was to slay the Maeonian Drakon every day.
- Eidolons – A race of spirits that can possess demigods. In The Mark of Athena, the Eidolons work for Gaea.
- Erymanthian Boar – The Erymanthian Boar is a giant boar, a servant of Pan who appears in The Titan's Curse. Percy, Thalia, Zoë, Grover, and Bianca first encounter it in Cloudcroft, New Mexico where Grover realizes its potential as a form of rapid transportation.
- Feather-Shooting Bird – A type of large black bird that shoots its feathers like arrows. In "The Demigod Files," Phobos summons them to fight Clarisse after he steals Ares' war chariot.
- Fire-Breathing Horse – A race of horses bred at the Triple G Ranch for war purposes. Some are shown to pull Ares' war chariot.
- Flesh-Eating Horse – A group of female horses bred at the Triple G Ranch. Some of them tried to eat Percy while he was cleaning the stables.
- Flesh-Eating Sheep – A race of carnivorous sheep owned by Polyphemus. They help to guard the Golden Fleece. Described as being a big as a hippopotamus and attacking like piranhas.
- Giant Badger – A giant badger. In "The Last Olympian," it was mentioned that Gleeson Hedge tried to fend off the Giant Badgers and tried to summon Pan to help him to do that.
- Giant Crab – A giant crab that might be Cancer. Percy fought it in the Princess Andromeda during his mission with Charlie. He defeated it by stabbing the soft tissue on its belly.
- Giant Eagle – A giant-size eagle that appears throughout The Heroes of Olympus series. The Giant Eagles are mainly used by the Romans for transporting and protecting Roman demigods.
- Giant Scorpion – A giant-sized scorpion. Daedalus (under the alias of Quintus) ordered some Giant Scorpions from the Triple G Ranch and kept them in their boxes in the Sword Fighting Arena. He eventually let them out in the camp's forest for a game.
- Giant Sea Turtle – A large sea turtle who accompanied Sciron into attacking the Argo II as seen in The House of Hades.
- Giant Snake – A large snake. It attacked Tyson and Grover when they were in the Labyrinth as seen in "The Battle of the Labyrinth."
- Giant Squid – A giant squid that might be the Kraken. It was among the sea monsters in Oceanus' army.
- Griffin – A Griffin is a creature that is part eagle, part lion. They appear in The Son of Neptune where they are seen in Alcyoneus' camp. They are not to be confused with the griffins of The Kane Chronicles.
- Hellhound – The Hellhounds are a main part of Luke's army and monsters in general. They are described as very large black dogs that have fire glowing in their eyes. They were also mentioned to reside in the Fields of Punishment. Daedalus owns a hound named Mrs. O'Leary, who, unlike her relatives, is loving and loyal. In "The Last Olympian," a bunch of Hellhounds are seen in Kronos' army where they snuck behind the demigod lines.
- Mrs. O'Leary – Mrs. O'Leary is the only friendly hellhound to ever exist. Quintus (an alias of Daedalus) was her original owner, but, after asking Nico di Angelo to kill him, Percy becomes the hellhound's owner. While Percy is in the "mortal world", Charles Beckendorf takes care of her at Camp Half-Blood. She rescues Percy while in the Labyrinth.
- Hippalectryon – The Hippalektryons are an endangered animal that is part chicken, part horse. In "Battle of the Labyrinth," they are seen at the Triple G Ranch.
- Hippocampus – Hippocampi are horses from the waist up with a fish tail from the waist down. One is said to take a liking to Tyson, and he named it Rainbow. They are also called "fish ponies" by Tyson.
- Rainbow – A Hippocamus who befriends Tyson in "The Sea of Monsters. Loves to give Tyson rides all over the sea.
- Hydra – A serpentine monster with nine heads. Every time a head is chopped off, two new heads grow back. This monster appears in The Sea of Monsters where its life force is linked to the Monster Doughnut Shop, as another one pops up every time the Hydra regrows a head. It was destroyed by the cannons of the CSS Birmingham. In The Mark of Athena, Percy fights a Hydra when he, Jason, and Piper are on a mission to rescue Nico from Ephialtes and Otis. In The Lightning Thief film, the creature takes the form of five janitors (played by Tom Pickett, Keith Dallas, V.J. Delos-Reyes, Spencer Atkinson, and Tim Aas) in the Parthenon replica in Tennessee and refers himself as "We." The Hydra is ultimately defeated by the use of Medusa's head.
- Karpoi – The spirits of the grain who are the size of toddlers. While many of them are malevolent thanks to their service to Gaea, children of Demeter are apparently also capable of summoning karpoi, although only one demigod has shown to possess the ability. In "The Son of Neptune," Percy Jackson, Hazel Levesque, and Frank Zhang encounter three Karpoi.
- Peaches - A friendly Karpoi that resembles a pudgy human toddler with green eyes and green hair. He is controlled by Meg McCaffrey.
- Keres – The Keres are battlefield spirits of famine and disease who feed on violent deaths. They reside in the Underworld and support the Titans but do not assist them in "The Last Olympian." In "The Demigod Files," some of them attacked Percy, Thalia, and Nico. One of them poisoned Percy, yet "Bob the Titan" managed to heal him.
- Katobleps – A race of cow monsters that appear in The House of Hades.
- Ketos – Chiron mentions this giant sea monster in "The Titan's Curse".
- Lemures – A race of angry ghosts who are seen on multiple times in The House of Hades.
- Leviathan – These are mentioned by Poseidon in "The Last Olympian" as giant sea creatures that are neutral in the war between Poseidon and Oceanus.
- Lupa – Lupa is the wolf that raised Romulus and Remus. She guides the children of Roman gods to Camp Jupiter after they are left for her at the Wolf House where she trains them to become Roman soldiers upon finding the worthy ones. She is the Roman counterpart of Chiron who does a similar job for the Greek demigods, only she is more militaristic. She appears in The Lost Hero and The Son of Neptune.
- Makhai – The Makhai are the spirits of battle and combat. In The Blood of Olympus, Asclepius used the Makhai and the Pylosian Mint in order to formulate a physician's cure.
- Mania – The Mania are ghosts that personify insanity, madness and crazed frenzy. In The Blood of Olympus, Beryl Grace and Julian Ramírez-Arellano are among the Mania.
- Myrmekes – A race of giant ant-like creatures who like shiny things like gold. In The Demigod Files, some Myrmekes trapped Charles Beckendorf in their nest. In The Hidden Oracle, Apollo and Meg come across a trio of Myrmekes who kidnap Meg, forcing Apollo to infiltrate their nest and rescue her. Later, Apollo successfully persuades the mother ant, "Mama", to help him and other demigods return to Camp Half-Blood.
- Nemean Lion – The Nemean Lion is a lion that is one of the children of Echidna and Typhon. It has a hard skin in which no weapon can penetrate. Luke and Atlas sent the Nemean Lion to the National Air and Space Museum to stop the group of questing Hunters and Demigods. It battled with Percy Jackson, but was hard to defeat because of its bulletproof and sword-proof pelt. Percy eventually defeated it by throwing astronaut food into its mouth thus exposing its one unprotected surface, its mouth.
- Nosoi - The Nosoi are the spirits of illness, plague, and disease that were originally locked up in Pandora's Box. In The Hidden Oracle, a bunch of Nosoi attack Apollo and Meg McCaffrey until they are fended off by them and the Karpoi Peaches.
- Ophiotaurus – A half-cow/half-snake monster. It was nicknamed Bessie by Percy Jackson who initially assumed it was female, although Grover later informed him that it was a male. Percy saved it from a trawler's net after being fetched by the Hippocampi. Bessie was supposedly the creature that Artemis was hunting because it could destroy Olympus. She/He appears in The Titan's Curse and The Last Olympian.
- Orthrus – A two-headed dog owned by Geryon and brother to Cerberus.
- Pegasus – Pegasi are winged horses that are named after the original mount of Bellerophon that was born from the blood of Medusa.
- Blackjack – He is the pure black Pegasus and Percy's loyal friend. He is first introduced in the second book The Sea of Monsters on the Princess Andromeda where Percy rescued him from Kronos's minions. Ever since then, Blackjack has felt like he has to pay Percy back for saving him and he does whatever Percy asks calling him "boss." He is seen in "The Blood of Olympus" delivering the Athena Parthenos to Camp Half-Blood.
- Guido – A light gray and white Pegasus who is friends with Blackjack. In "The Last Olympian," Guido and Porkpie aided Percy and Blackjack in the Battle of Manhattan. Guido later adopts Reyna for his human after the Giant War.
- Porkpie – A light gray and white Pegasus who is friends with Blackjack. In "The Last Olympian," Guido and Porkpie aided Percy and Blackjack in the Battle of Manhattan.
- Scipio – Reyna's Pegasus who appears in The Son of Neptune. His nickname is "Skippy" because he's the color of peanut butter (the same color as chestnuts). He died at the end of "The House of Hades" because of a gryphon strike.
- Pit Scorpion – A deadly type of scorpion that appears in "The Lightning Thief." When Luke brings Percy into the woods and reveals his allegiance to Kronos, he summoned a Pit Scorpion to attack Percy. He tells Percy he should not go for his sword, as the pit scorpion can kill in sixty seconds, and can jump up to fifteen feet. When Luke disappears, Percy manages to kill it even though it managed to sting him. Wood nymphs help Percy recover from its poison.
- Scylla – One of the two monsters (the other being Charybdis) who live on either side of a narrow channel of water in The Sea of Monsters. Should a ship sail too close to her, she uses her six heads to pluck off crew members on deck and devour them. According to Clarisse (daughter of Ares), Scylla would just pick up the whole boat and crushed the boat if the crew hid below deck. In the film Percy Jackson: Sea of Monsters, Scylla was mentioned by Clarisse to have eaten Ichneutae.
- Sea Serpent – A large serpent that lives in the sea. Deimos is seen riding one in "The Stolen Chariot." In "The Last Olympian," a sea serpent was seen amongst the sea monsters in Oceanus' army.
- Sirens – The Sirens are dangerous bird women whose sweet songs lead many sailors to their deaths on the jagged rocks. In The Sea of Monsters, they almost killed Annabeth.
- Skeleton – Skeletons are the undead troops that make up Hades' Undead Army. In "The Lightning Thief," Hades has skeletons in army uniforms guarding his palace. In "The Battle of the Labyrinth," Nico manages to employ them as part of a ritual that will enable him to call the spirit of his sister to speak with her. In "The Last Olympian," Nico and Hades manage to bring a troop of skeletons to help fight the Titans. They are later seen constructing a cabin at Camp Half-Blood which is dedicated to Hades. In the House of Hades they are on the demigods side and help them in the Hades's temple in Epirus.
- Skolopendra – A sea monster that is 200 ft. long. It looks like a cross between a giant shrimp and a cockroach with a pink chitinous shell, a flat crayfish tail and millipede-type legs. Its face is a slimpy pink like an enormous catfish with two glassy dead eyes and a gaping toothless maw. It has a beard which has a numerous amount of tentacles sprouting from each nostril. In The Mark of Athena, Ceto sents Skolopendra after the demigods after their escape from Phorcys' aquarium. It attacked the Argo II when Leo forgot to turn the monster-detection system on. Percy describes Skolopendra as "shrimpzilla." Skolopendra withdraws into the ocean when Leo Valdez and Hazel Levesque throw test tubes filled with Greek Fire into its mouth.
- Spartus – A troop of skeletons armed with weapons. They are usually summoned by planting dragon (Sybaris) teeth in the ground and watering them with blood. In The Titan's Curse, some Spartoi ambushed Percy, Thalia, Zoe, Grover and Bianca in New Mexico. Due to her being a child of Hades, Bianca managed to destroy them. In The Son of Neptune, Frank (as a gift from his father) is given a spear with the tip of a dragon's tooth that when planted with raise one of the Spartoi, he uses this to defeat the basilisks outside of the R.O.F.L. headquarters, to kill some of the laistrygonians surrounding his grandmothers house then using his final charge to protect the mortals on a train from attacking Griffins.
- Gray - A Spartus that can be summoned by Frank Zhang.
- Sphinx – A Sphinx is a monster with the head of a woman and the body of a lion. Percy Jackson and his friends encountered the Sphinx while navigating the labyrinth. Rather than tell riddles, the Sphinx asked historical questions which Annabeth refused to answer as an insult to her intelligence. They are not to be confused with the Sphinx from The Kane Chronicles.
- Stymphalian Birds – A flock of birds once attacked Camp Half-Blood in The Sea of Monsters. Percy and Annabeth used Chiron's music to scare them so Apollo's cabin could shoot them down. A flock of Stymphalian Birds attack the Argo 2 in "The House of Hades."
- Telekhine – The Telekhines are a race of dog-faced sea demons that reforged Kronos's blade in the fourth book. Some set Percy on fire in the fourth book. They also appear in the fifth book. In the fourth book, they are referred to as "telekhines." However, in the fifth book, they are referred to as "telkhines", without the second "e". This may be a typographical error or something different of the author's choice. In The Mark of Athena, some Telekhines are seen in a water tank at the Georgia Aquarium.
- Trojan Sea Monster – A type of sea monster that rampaged the coasts of Troy until it was slain by Heracles. It is also known as the Keto Trois. In The Lost Hero, Jason Grace claims to have slew this monster while fighting Porphyrion of the Gigantes.
- Typhon – A very powerful monster. He sired many monsters by Echidna. He lives and sleeps inside Mount Saint Helens. Percy is such a powerful demigod that he almost wakes Typhon during his visit there. In The Last Olympian, Typhon awakes and moves across America destroying everything in his path. As he is concealed in mist, Typhoon's appearance is not described and appears as a freak storm. The gods of Olympus try to stop him, but he is too powerful. In the end, Poseidon and his army help defeat him where Poseidon opened up a tunnel that sends Typhon into Tartarus. Once Typhon was defeated, a wave of anemoi thuellai were born.
- Unicorn – A horse with one horn. A herd of Unicorns are used as steeds for the campers of Camp Jupiter. A red-tinted Lares with the head of a wolf guards them.
- Venti – A race of storm spirits that were born when Poseidon opened a tunnel that sent Typhon into Tartarus. Depending on how chaotic they are, Venti can appear as either smokey men with angel-like wings or smokey horses. In The Lost Hero, Aeolus sent the Venti to prevent Jason, Piper, Leo, and the Hunters of Artemis from rescuing Hera. Their Greek counterparts are anemoi thuellai.
- Dylan – A ventus that was among the Venti that attacked Jason Grace, Piper McLean, and Leo Valdez as seen in The Lost Hero.
- Tempest – A ventus in smokey horse form that appears in The Lost Hero. Jason tames Tempest so that it can help him fight Porphyrion.
The Kane Chronicles
Carter Kane is one of two main protagonists and narrators; a descendant of Narmer and of Ramses the Great. He is the son of Julius and Ruby Kane. After the death of his mother (when he was eight years old), he spent six years travelling the world with his Egyptologist father. After his father is captured by the god Set during The Red Pyramid, Carter spends most of his time with his sister Sadie and uncle Amos Kane. He becomes the host of Horus in the first novel, and often collaborates with and receives advice from the god. He also develops a romantic relationship with the shabti of magician Zia Rashid, and subsequently spends much of his time trying to find the real Zia and demonstrate his feelings toward her. Like his father, Carter has dark skin and hair, quite different from both his mother and sister. When living with his father, Carter dressed "impeccably" like Julius even when relaxing, but adopts a much more casual style when he goes to live at Brooklyn House. Though he is not one to flout rules, Carter is brave and courageous enough to pursue the way of the gods despite the House of Life's disapproval. His specialty is combat magic; his preferred weapon a khopesh. He is often given leadership responsibilities and struggles to accept his role, until he willingly becomes pharaoh of the House of Life during The Serpent's Shadow.
Sadie Kane is one of two main protagonists and narrators; the younger sister of Carter Kane. She is left in the care of her non-magical grandparents in London after the death of their mother Ruby Kane. Though she is able to live a "normal" life, something her brother is occasionally jealous of, her unusual circumstances make her sometimes jealous of Carter (especially when she is reminded of his exotic lifestyle). Sadie has to abruptly leave her life in London when she goes to revive the twenty-first Nome and fight Set after the god captures her father, Julius Kane. Sadie becomes the host of Isis in The Red Pyramid and continues to study the goddess's path throughout the series. She also becomes romantically involved with one of the Brooklyn House initiates Walt Stone and also with the god Anubis, though her relationship with either is not formalized until after Walt becomes the "eye" of Anubis in The Serpent's Shadow.
She has caramel-colored hair and light skin, traits inherited from her mother Ruby. Unlike Carter, Sadie is rebellious and bold (also like her mother) and acts the part; often making snap decisions, ignoring rules, and choosing to wear clothing to display her personality rather than to conform or aid her magic. Her magical specialty is with spells, potions, and hieroglyphics.
Walt Stone is one of the twenty-first Nome's initiates, who arrives at Brooklyn House sometime between the first and second novels. He has dark skin and is from Seattle, where he lived with his mother. Walt is a sau, or charmmaker. In The Throne of Fire, it is revealed that Walt has inherited a deadly curse from his ancestor Akhenaten, which will kill him before reaches adulthood, as it did to his father and their famous ancestor King Tut. The curse progresses more quickly when he uses magic, which is why he specializes in charms and also why he begins to call on the god Anubis for guidance. In The Serpent's Shadow, Walt finally succumbs to the curse, but as he dies he allows himself to become the host of Anubis, whose spirit can essentially keep him alive. Both Anubis and Walt Stone have romantic feelings for Sadie Kane, and this is part of the reason why the two "fuse" successfully.
Zia Rashid is a magician from the first Nome who was born and raised in Egypt. She is found and raised by Iskandar, the Chief Lector, after the destruction of her hometown by Apophis. When Julius Kane released five gods through the Rosetta Stone, she became the unexpected host of Nephthys, and was subsequently placed by Iskandar in an underwater prison so the House of Life could not eliminate her. A shabti of her was created to take her place; it is destroyed during the fight with Set in The Red Pyramid. Carter Kane falls in love with this shabti and seeks out the real Zia to free her and release Nephthys's spirit. Zia, who specializes in fire magic, later becomes the host of Ra and the two manage to destroy Apophis in The Serpent's Shadow. Her initial indifference to Carter slowly evolves into romance, and the two begin dating at the end of the series when Ra ascends back to the heavens.
Amos Kane is Julius Kane's younger brother, Carter and Sadie's uncle, and the leader of the twenty-first Nome (New York). He takes in Carter and Sadie after Julius hosts Osiris and is trapped by the god Set. During the first novel, Amos is possessed by Set and forced to lure his niece and nephew to the god's pyramid in Phoenix, Arizona. Once freed, Amos goes for healing at the first Nome, and does not return to Brooklyn House until the second novel. His experience hosting Set has changed him, however, and eventually leads to his highly controversial decision to voluntarily host the god during the final battle with Apophis. Amos succeeds Michel Desjardins when the former leader of the House of Life sacrifices himself fighting Apophis.
Iskandar is the Chief Lector of the House of Life. Born in the 1st century BCE, during the reign of Cleopatra VII, he witnessed the end of the Egyptian monarchy and the absorption of Egypt into the Roman Empire. He came to believe this was the fault of the gods and ended the House's policy of calling upon them; Ruby Kane's vision of Apophis rising changes his mind, but it is too late for him to make any real change. He was the one who saved Zia after her village's destruction and, sensing that she holds the power to host Ra, arranged for her confinement in an underwater prison under the watch of Nephthys while creating a shabti of her to protect Carter and Sadie, both of whom also hold the potential to become hosts of gods. Shortly after meeting them, he dies in his sleep, knowing that these three can make a change where he could not. He is succeeded by Michel Desjardins as the House's leader.
Michel Desjardins is the lesser antagonist and leader of the House of Life after the death of Iskandar. Desjardins is the grandnephew of Jean-François Champollion and approximately 200 years old, considered "young" for a magician. As such, he has known only the House policy forbidding the Path of the Gods. He is therefore at first opposed to cooperation with the gods and disagrees with the Kanes when they claim it is necessary to stop Apophis. He works with Vladimir Menshikov in the latter's attempt to hunt Sadie and Carter Kane, believing his lies about how the Kanes' efforts will empower Apophis. Upon discovering the truth, that the Kanes were right and Menshikov is trying to free Apophis, he journeys to the Duat to help Carter and Sadie and sacrifices himself to execrate Apophis, killing Menshikov and buying the Kanes more time. He is succeeded as leader of the House of Life by Amos Kane.
- Anubis — God of funerals and death and periodic advisor to Sadie Kane, for whom he has romantic feelings. Walt Stone becomes his host in The Serpent's Shadow. Anubis is the son of Nephthys and Set, but felt closest to his uncle Osiris, who raised him in Duat.
- Apophis — The serpent of chaos who fought Ra in ancient times. Throughout the series, he possesses demons and other characters in attempts to break free of his prison (a place deep within the Duat where he once battled Bast for eternity). He breaks free of his prison in The Throne of Fire, but is execrated by Michel Desjardins. He does so once again in The Serpent's Shadow, but is held at bay through the combined efforts of many gods and magicians.
- Babi — Egyptian baboon god who takes Mr. Faust as host, helping Nekhbet test Sadie Kane.
- Bast - The cat goddess and Ra's guardian. In ancient times, she was sent by Ra to fight Apophis after the latter ascended to the heavens, which she continues to do until Julius and Ruby Kane release her. She then takes as host a cat named "Muffin" and makes a pact to guard Sadie. Bast then becomes Carter and Sadie's guardian after the two become magicians, and becomes quite close to them, considering them her "kittens". In The Red Pyramid, she sacrifices herself fighting Sobek to protect the injured Sadie, but is brought back from Duat by the gods as reward for the Kanes (after they defeat Set).
- Bes — God of dwarfs and protector of the innocent. He has romantic feelings for Bast, and answers her request that he watch over Carter and Sadie. He befriends the two and sacrifices his ren to give them enough time to reach Apophis's prison. The two later manage to restore him, and he goes on to pursue a relationship with the goddess Tawaret.
- Geb — God of the earth. Father of Osiris, Isis, Horus, Set, and Nephthys; husband of Nut. His physical manifestation is the entire earth.
- Hapi — God of the Nile river. In The Serpent's Shadow, he is summoned by Carter using a spell from Setne, and asked to defeat a monster sent by Apophis. Hapi also helps Carter and Zia cross the Nile to reach the temple of the Apis Bull. Hapi is described as huge, blue-skinned, and well-fed.
- Heket — An ancient goddess of frogs who lost her power when her temples were destroyed and people stopped worshiping her. She is currently living in Sunny Acres Assisted-Living Community, a place for senile gods and goddesses, as revealed in The Throne of Fire.
- Horus — God of war; Leader of the gods until Ra's return, and again after Apophis is destroyed. Part of his spirit resides in Carter Kane. His symbol is the Eye of Horus. He is one of the five gods born during the Demon Days (the five days at the end of the solar calendar that account for its not being an even 360 days long), the son of Geb and Nut. He is also frequently described as the son of Osiris and Isis.
- Isis — Goddess of magic; briefly incarnated by Sadie and Ruby Kane; her symbol is the Tyet. She is one of the five children of Geb and Nut, and the mother of Horus. She is responsible for Ra's ascendance from the mortal world. When she wanted her husband Osiris to claim Ra's throne, she created a serpent to poison Ra. When he revealed to her his secret name, she cured him but also forced him to abdicate the throne.
- Khonsu — Moon god. He was a trickster who liked to play senet, a board game, with deadly bet in return for a lengthened time; Nut once played a game with him so she could gain enough time to give birth to her five children. In The Throne of Fire, the Kanes and Bes played senet with him so they could gain more time for the gates of Duat to open; when they lose a round, Bes sacrificed his ren, which caused him to lose his memories until the Kanes managed to find his sheut in The Serpent's Shadow.
- Mekhit and Onuris — Two war gods who were forgotten by humans and thus had to live in Sunny Acres. Onuris disappeared due to his senility, which made Mekhit mournful. He is found again in The Serpent's Shadow, and later fights alongside his wife with the retired gods who helped the Kanes.
- Neith - Goddess of the Hunt. She loves weaving. She makes a brief appearance in The Serpent's Shadow when Sadie and Walt trick her into helping them.
- Nekhbet — Egyptian vulture goddess who takes Mrs. Faust and Percy Jackson as hosts. She is a follower of Ra, but refuses to follow the weak. As a result, she "tests" Sadie Kane's strength by attempting to kill her, her family, and her friends. It is revealed in The Crown of Ptolemy that Nekhbet possesses the crown of Upper Egypt, which Setne steals, although she manages to avoid Wadjet's fate of having her essence absorbed thanks to the heroes. She proceeds to assist them in order to recover her crown.
- Nephthys — Goddess of rivers; wife of Set, mother of Anubis, and one of the five children of Geb and Nut. She was once incarnated by Zia.
- Nut — Ancient Egyptian sky goddess; mother of Osiris, Isis, Horus, Set, and Nephthys. Wife of Geb. Due to a prophecy that one of her children would unseat him, Ra forbade Nut to give birth on any day of the year. She gambled with the god Khonsu to earn five extra days worth of moonlight to have her children and was punished by Ra. He forbade her to ever see her husband again, and tasked her father Shu with keeping them apart. Her physical manifestation is the sky itself.
- Osiris — Ancient Egyptian god of the dead; incarnated in The Red Pyramid by Julius Kane. He is one of Geb and Nut's five children. His symbol is the 'Spine of Osiris', or the djed. He is frequently described as having blue skin, representing the fact that he is "dead". He was once king of the gods until his brother Set imprisoned and later killed him. His wife Isis and sister Nepthys searched for his body to revive him with magic, but were only able to make him pharaoh of the Duat.
- Ptah — God of craftsmen and creation, summoned by Sadie and Walt help get a piece of the Book of Ra.
- Ra — Sun god. Retired to the heavens, but revived in The Throne of Fire; later merges with Zia and recovers his lost mental integrity. Consumed by Apophis and later revived by Sadie and Carter. He was the first and greatest king of the gods, and undertook nightly journeys through the Duat (as the sun sets and rises) to battle the forces of chaos.
- Khnum — Ra's evening aspect who created man out of clay using a potter's wheel. In The Throne of Fire, the Kanes meet him near the entrance of the Duat and have one chance to guess his name, which he had forgotten after so long. Sadie eventually gave him his ren, which was what he was really looking for, and he allows them to pass on to revive his other aspects.
- Khepri — Ra's morning aspect that had the form of a golden beetle. The Kanes found it near the exit of Duat and had to battle Valdimir Menshikov, possessed by Apophis, in order to give it to Ra and thereby restore his final aspect.
- Set — Ancient Egyptian god of evil. Antagonist of The Red Pyramid, and a supporting character in The Throne of Fire and The Serpent's Shadow. He is one of Geb and Nut's five children, born on the last Demon Day, and is married to Nephthys. He was once Ra's "faithful lieutenant" against the forces of Isfet, but became the embodiment of chaos after Ra's ascension. His secret name is 'Evil Day'.
- Sekhmet — Goddess of lions. She can be summoned by a Chief Lector once in his/her lifetime, and attacks Carter, Sadie, Zia, and Amos at the command of Michel Desjardins. She is the warlike lieutenant of Ra and a master of destruction.
- Hathor — Goddess of cows, also the alter-ego of Sekhmet. She is summoned whenever Sekhmet is tired, and represents the goddess's peaceful side.
- Serqet — Goddess of scorpions. In The Red Pyramid, she attacked Carter, Sadie, and Bast after the three had escaped from Brooklyn House, forcing Bast to retreat while the Kanes were saved by Zia.
- Shezmu — God of execution. In The Red Pyramid, he prevented the Kanes from entering Duat unless they told him his secret name, though he ended up revealing it to Sadie while the three compromised.
- Shu — God of the Air; The father of Nut and Geb, who separates Nut from Geb to form the present-day division of Sky from Earth. Later appears to criticise Anubis' infatuation with Sadie.
- Sobek — God of crocodiles; appears as a minor antagonist in The Red Pyramid but later aids Ra against Apophis.
- Tawaret — Egyptian goddess of hippos and childbirth, assists the protagonists. As a protector of the innocent (specifically children), like the god Bes, she is very familiar with him and has romantic feelings for him. At first these are unreciprocated as he is in love with Bast, but he comes to appreciate and care for her after she takes care of him when he has lost his ren. Tawaret is the sole nurse in the Sunny Acres retirement community for old gods, located in the Duat.
- Thoth — God of knowledge and founder of the House of Life. "Thoth" was actually his Greek name; Egyptians called him Djehuti. He is the only god who is accepted by the House of Life and is allowed to inhabit the mortal world; he is found in Memphis, Tennessee in various locations. Carter and Sadie seek him out for advice on two separate occasions.
- Wadjet - A cobra goddess who makes a brief appearance in The Crown of Ptolemy where Setne summons her, steals her crown of Lower Egypt, and then steals her essence, killing her.
Brooklyn House trainees
- Jasmine 'Jaz' Anderson — One of the novitiate magicians in Brooklyn House. She is a blonde, sixteen year-old cheerleader from Nashville, Tennessee. Her specialty is healing magic and studies the goddess Sekhmet as all Egyptian healers do. She is put into a coma after banishing some sickness demons in The Throne of Fire, from which she is awakened by Ra. She shares with Sadie how to cure Carter using his ren when he is bitten by a tjesu heru. She later appears in The Serpent's Shadow and her healing potions appear in the crossover stories The Son of Sobek and The Staff of Serapis.
- Alyssa - A trainee of the twenty-first Nome with a particular skill for pottery and shabti-making. She studies the power of Geb.
- Cleo - One of the young magicians at Brooklyn House. She is from Rio de Janeiro. Cleo studies the god Thoth and will likely be Brooklyn House's next librarian. Though she is an excellent researcher, she does not have much of a stomach for violence.
- Felix - A 10-year-old trainee at Brooklyn House. He has a strange obsession with penguins and seems to be able to channel ice magic, though it is unknown which Egyptian god this corresponds to.
- Julian — A seventh-grade trainee. Like Carter, he incarnates the power of Horus.
- Sean - An Irish trainee at Brooklyn House.
- Shelby - A very young trainee at Brooklyn House, the ringleader of the group of toddler trainees known as the "anklebiters". Her magic is mostly impulsive.
- Leonid - A young Russian magician who first encountered the Kanes when they visited Saint Petersburg. He defects to the "side" of the gods and, with the help of the god Shu, brings Sadie and Carter information during book three.
- Julius Kane — Carter and Sadie's father, and a doctor of Egyptology. After a failed attempt to release the Egyptian goddess Bast back into the world results in the death of his wife, he works to find a way to release them again and become host to Osiris. He ultimately succeeds, dies of his own free will, and goes to "live" as the god's physical manifestation in the Underworld, overseeing the Hall of Judgment.
- Ruby Kane — Carter and Sadie's late mother, who appears occasionally as a ba to advise her children. She was a magician and diviner who foresaw Apophis's rise and ultimate victory if the other gods were not there to stop him. As a result, she and her husband attempted to release Bast from her eternal battle with Apophis so the goddess could heal before his inevitable rise. She gave her life to close the portal they opened using Cleopatra's Needle, because Apophis was fighting to get out. Ruby also communed with Isis at some point in her career as a magician, and attempted to convince then-Chief Lector Iskandar to remand his policy of fighting the gods.
- Vladimir Menshikov — The antagonist of The Throne of Fire. Menshikov's intense hatred of the gods and desire for power leads to his possession by Apophis. He manipulates Michel Desjardins into permitting him to hunt the Kane family. When Desjardins finally discovers his involvement, he uses up all his energy in an execration of the chaos demon and, by extension, Menshikov, who is then killed. Menshikov is described by Sadie and Carter Kane as an "evil ice cream man" because of his tendency to wear white suits and glasses because of his heavily scarred face.
- Setne - An evil magician and son of Ramses the Great. He is also known as Khaemwaset. He appears in The Serpent's Shadow as an evil ghost on trial for many crimes. Setne is freed by the protagonists Carter and Sadie to aid in the fight against Apophis. After the former's destruction, however, Setne escapes and becomes the main antagonist of the crossover series with the Camp Half-Blood chronicles, where he plans to amass the power of both the Egyptian and Greco-Roman worlds. He is finally trapped in a snow globe by Carter, Sadie, Percy Jackson, and Annabeth Chase.
- Sarah Jacobi - The leader of a group of rebel magicians, a former House scribe imprisoned for causing the 2004 Indian Ocean earthquake and tsunami. In The Serpent's Shadow, she manages to amass an alliance of rebels in league with Apophis, but is vanquished by Anubis/Walt Stone, who bury her underground.
- Kwai - Sarah Jacobi's assistant, the House of Life's persistent opponent throughout the later books and also a brief host of Apophis.
- Ammit the Devourer — A part-hippo, part-crocodile, part-lion demon who devoured souls that were judged unworthy in the Halls of Judgment. The Kane Chronicles present a different picture of Ammit than is typical, by portraying the demon as both no larger that a toy poodle and as a male. In Egyptian myth, Ammit was both female and an enormous fearsome monster. In The Throne of Fire, "he" is nicknamed "Poochiekins" by Sadie.
- Doughboy — Julius Kane's wax shabti; comically resentful of Julius. He is used for many purposes by Carter and Sadie.
- Freak - Carter's pet griffin. It was initially a statue brought to life by Sadie. Tamed by Carter in The Throne of Fire (because the griffin is a sacred animal of Horus); his pet and personal transportation thereafter.
- Khufu — Amos's pet baboon. Like many baboons in the series, he loves basketball and speaks only in monosyllabic grunts. Khufu's other quirk is that he only eats things that end in the letter 'O', such as Cheerios, Jell-O, and flamingo meat.
- Leroy - The Set animal that was destroyed and nicknamed by Carter Kane.
- Mummy - The Mummies are undead bodies that are wrapped in bandages. They can be summoned through Egyptian necromancy.
- Philip of Macedonia — Amos's albino crocodile pet, later identified as a wax shabti. Protector of and (briefly) transporter for the protagonists.
- Serpopard - The Serpopard is a controlled creature of chaos that has the head and neck of a snake and the body of an African leopard. They have the ability to spit poison and are tremendously strong.
Magnus Chase and the Gods of Asgard
Magnus Chase is the main protagonist of the series. A 16-year-old Bostonian teenager, Magnus lost his mother Natalie to a mysterious wolf attack two years prior to the events of The Sword of Summer and is forced to live in the streets with his homeless friends, Blitz and Hearth. On his 16th birthday, his uncle, Randolph informs him of his divine parentage as a son of a Norse god and his inheritance of Sumarbrander, the sword that once belonged to his father Frey. After being killed by Surt, a fire giant, Magnus is then carried to Hotel Valhalla by Samirah Al-Abbas, a Valkyrie. He then finds out that his father is Frey, the god of peace, wealth and prosperity, who belongs to the Vanir tribe of Norse deities.
Magnus is described as having blond hair that reaches his chin and haunting gray eyes that resemble his cousin, Annabeth's. He is said to look like Kurt Cobain and has asthma. His scrawny look is replaced by a more muscular persona after his death and acceptance to Valhalla. He is quite street smart due to the two years he spent as a homeless man and as a result, is not quick to trust people. Nevertheless, he considers Blitz and Hearth as the only friends he is completely loyal to, and after a while, also begins to ease up and trust Sam. He is also known to have a budding relationship with another child of Loki named Alex Fierro. He is not fiery nor quick to anger.
As a son of the god of fertility, Magnus does not excel in offensive power. Instead, he usually thinks strategically to safely escape from danger. When he does have to attack, he mainly uses the Sword of Summer, Jack, who attacks autonomously. Magnus' demigod abilities concern healing and warmth: through concentration, Magnus is able to heal even the mortally injured as well making a mortal see through Ginnungagap and thus the Norse world, though doing so often causes him to read the subject's memories.
Blitzen (Blitz) is a 20-year-old dwarf or, more specifically, a svartalf from Nidavellir. He has dark skin and hair, and has a beard. He is the son of a Vanir, Freya, making him Magnus' cousin, and a dwarf, Bilì, who was eaten by Fenris Wolf while checking Fenris's prison rope. He is sent alongside Hearth by Mimir to watch and protect Magnus. Though he keeps it up for two years, the task fails when Magnus is killed, but Blitz continues to look for him until they are reunited in Valhalla. As a dwarf, Blitz is sensitive to sunlight and will slowly turn to stone if exposed too much, which is why he always wears a copious article of clothing whenever there is sunlight, except in Folkvanger, in which sunlight is replaced by an aura radiated by Freya instead. Instead of forging, Blitz excels in clothing design, making him a laughing stock among his fellow dwarfs, but after he wins a match against Eitri Junior, he becomes respected and eventually opens up a clothing shop. In battle, Blitz uses his creations to assist himself, including chain-mail gloves and vest. Blitz has had a strong relationship with Hearth ever since the former saved the latter's life, and the two are very protective of each other.
Hearthstone (Hearth) is a light elf from Alfheim. He is skinny with fair skin and with short spiky white hair, which, when combined with his black leather jacket, jeans and a red scarf, "makes him look like a character from a Japanese anime". Hearth is deaf and can only communicate with ASL (Alf Sign Language), though he is able to read lips. Since his home world is always bright, he is sensitive to darkness. Like Blitz, Hearth makes a deal with Mimir to drink water from Mimir's Well by one of the roots of Yggdrasil to gain knowledge about runes and in return has to work with him for several years. He becomes a companion and protector of Magnus from then on. Hearth is the first elf in a long time to focus on magic from runes, which he has studied extensively. He can cast various runes, though doing such consumes his energy. Eventually he progresses to the rank of a full sorcerer. Hearth has a traumatic past, as he is effectively unwanted by his parents, who shun him for being deaf and not as great as his brother, Andiron, who died young; he is forced to face his past in the second book, when he has to collect the Skofnung Stone from his father, Alderman, who wants him to finish the blood tax imposed on him as repentance for Andiron's death. He is also reminded that sooner or later, he will have to take the othala rune from Andiron's place of death, which he planted as a reminder of his past, to complete his magic arts. His relationship with his friends helps him, though, and he even once calls Magnus "brother". At the end of the first book, Hearth is freed from servitude and begins learning runes at Asgard from Odin.
Samirah (Sam) al-Abbas is a Valkyrie and a daughter of Loki who selects Magnus as an einherji under Odin's order. She is an Arab American who normally wears her Valkyrie armory and a noticeable green hijab, which also functions as a swan cloak, or an invisibility cloak. As a Valkyrie, Sam is different from Magnus in that she is still alive. She leads a double life as both a Valkyrie and a normal high school sophomore. She does not worship the Norse gods as she already has a God she believes in, though she still has to occasionally work with them. Her family is from Baghdad, Iraq, and Sam is raised by her grandparents in Dorchester after the death of her mother Ayesha. Sam's family already had a long history with the Vikings, even before her mother met Loki; Ahmad ibn Fadlan, an envoy of the Abbasid Caliph to the Kievan Rus', is one of Sam's ancestors, and the Varangians had since intermarried with Sam's family. Her parentage is a shame to both sides of her parents; she is shamed in her mother's family as an out-of-wedlock child, while having Loki as a father makes others view her as suspicious among the Asgardians. Sam has an interest in flying and planes and vows to become a pilot one day, which is why she is very serious about her job as a Valkyrie.
In The Sword of Summer, Sam is expelled from Valhalla when her video of Magnus' heroic death is edited by Gunilla, but later joins Magnus, Blitz, and Hearth in stopping Fenris Wolf from breaking free. She is eventually reinstated as Valkyrie and gets another job as Odin's personal aide. In The Hammer of Thor, Sam is betrothed by Loki to Thrym in exchange for Mjolnir; in reality, Loki wants the Skofnung Sword, with which he can finally free himself. Sam is then given a task by Odin to head towards Scandinavia and personally imprison Loki back before he is able to invade Midgard, and eventually invade Asgard.
As a fighter, Sam excels in using the axe, a weapon of the Valkyries. She also inherits her father's ability to shapeshift into animals such as a horsefly or lion (her surname, al-Abbas, means 'of the Lion' in Arabic); however, it makes her uncomfortable, as it causes her to become more like her father, Loki.
The Sword of Summer (Jack) was Frey's weapon, currently wielded by Magnus Chase. After Magnus finds out that the sword is sentient, Sumarbrander decides to name itself Jack, and be referred to as a male. In battle Magnus can let the sword attack his enemies on its own or use his own strength and control the sword himself. Either way, it is Magnus who loses energy ultimately, though this loss is delayed until he next grips or sheathes Jack.
He bears a grudge against Frey, who 'abandoned' him, by giving him to Skirnir as a price for the latter bringing the former a Giantess with whom he fell in love; he summarises this by once admonishing Frey, saying 'blades before babes'.
He reached Boston with one of Skirnir's descendants during the Viking expansion, where he was lost for centuries till he was recovered by Magnus.
Introduced in Magnus Chase and the Hammer of Thor, Alex Fierro is a child of Loki and Mr. Fierro. She is gender-fluid, similar to Loki who was known to change genders in myths. When in Valhalla, she is referred to as an argr, the Old Norse word for Unmanly, due to being born a male but identifying as a woman occasionally. Unlike her half-sister, Sam, Alex was born via Loki's female form, thus making the god her mother rather than her father. Like Sam, she resents her mother; however, Alex seems to be able to resist Loki much easier than Sam. She, like Magnus, is homeless due to her family disagreeing with her gender-fluidity.
Alex uses a gold garrote wire as a weapon, which formally used to be a pottery wire. She can also shape-shift into things such as a bear and an elephant in combat, and is far more comfortable with embracing this power than her half-sister, Sam.
The Norse gods fall into two general groups: the Aesir and the Vanir. All are referred to generally as "Asgardians", but the Vanir inhabit Vanaheim as often as Asgard. The Aesir are more warlike, while the Vanir are peaceful. Specifically, however, the gods tend to be distinguished by what side they fought on during the Aesir-vanir war, and not by their personal temperaments.
The following Norse gods are considered the more warlike of the two strains of immortals.
- Heimdall – Heimdall is the all-seeing, all-hearing god of vigilance and guardian of Bifrost, the entrance of Asgard, who was born from nine mothers. He has a hobby of taking selfies, using his horn Gjallar as a phablet and a selfie stick, which tends to make him forget to directly oversee the Nine Worlds.
- Loki – Loki is the god of evil and trickery. He is the father of Samirah Al Abbas. He can also become female, having turned into a mare to give birth to the eight-legged horse Sleipnir and later into a red-haired woman to give birth to the demigod Alex Fierro, who like Loki, is genderfluid. After tricking Hod to kill Balder, he is chained to a rock with the entrails of his sons as chains with poison from a snake dripping onto his face constantly. He makes it his personal goal to break free and take revenge against the gods in Ragnarok, using his trickery to manipulate people around him even when he is incorporeal. He finally manages to break free at the end of The Hammer of Thor.
- Mimir – Mimir is the god of knowledge and wisdom. He was beheaded during the Æsir-Vanir War and only his head remains. He is the boss of Blitz and Hearth due to a deal they made, in order to drink from his well. The deal is nullified by Odin at the end of first book as their reward for dealing with Fenris Wolf.
- Odin – Odin, the "All-Father", is the king of the Aesir, the god of royalty and magic. He is able to rewrite reality by spelling out runes, which he learned after hanging for nine days on a branch of Yggdrasil. In The Sword of Summer, Odin is claimed to have disappeared two years before Magnus' acceptance as an einherji, but he actually disguises himself as X, the son of a troll, and one of Magnus' floormates. At the end of the book, Odin reveals himself and rewards Magnus and his friends for their bravery against Fenris Wolf. He likes to give presentations.
- Ran – Ran is the goddess of the sea, who operates a net that collects anything that falls into the sea, including tools, trash, and souls. She has an apple of Idun, but forgets to consume it, which contributes to her elderly appearance. Magnus and Sam manage to convince her to give them the apple and Sumarbrander, but she warns that doing so has made her and Aegir bent on attacking Magnus.
- Sif – Sif is the goddess of the earth and Thor's self-proclaimed "trophy wife". After losing her hair due to Loki's trick, she now has golden hair that can be melded into precious objects, inspiring the legend of Rapunzel. Sam and Alex, both Loki's children, do not like her; the former states that Sif is vain and accepts her hair replacement and title because she does not understand that Loki is merely playing with her. Alex, however, begins to have respect for her after she helps her dress for Thrym's wedding ceremony.
- Sigyn – Sigyn is Loki's wife. She reduces his punishment by collecting venom dripped by the venomous snake in a bowl, though it is never enough to alleviate them from torturing him. When Loki is about to free himself in The Hammer of Thor, she appears to make an attempt to delay the escape, but later goes with him anyway when the Asgardians come. She is described as having red eyes that tear blood, as well as a perpetually blank expression.
- Thor – Thor is the god of lightning, storms, and strength. He has an unkempt appearance, is lazy, and is also up-to-date with modern television shows. He has red hair, huge muscles and a dirty face. He wears a sleeveless, leather jerkin and is very loud. He tasks Magnus and his friends with retrieving his spear, which was stolen from him by Geirrod. He has two talking goats, Tanngrisnir and Tanngnjostr, nicknamed Otis and Marvin. His hammer is currently missing, which becomes an important plot point in The Hammer of Thor, where he regains it.
- Vidar – Vidar is the god of revenge, also called the "Silent One" due to his method of communicating with ASL. He is sensible and snarky, a complete opposite of his brother Thor.
These gods are generally more peaceful and dislike the warlike nature of the Aesir.
- Freya – Freya is the goddess of love and warmth and the twin sister of Frey. She is described as very beautiful. She presides over Vanaheim, where the other half of worthy souls go after death, and casts warmth that shines over it. Freya is the mother of most dwarves in Nidavellir, including Blitz, which happened because she bartered to (briefly) marry some dwarves in exchange for luxurious items. Freya tasks Blitz to get some earrings by challenging Junior.
- Frey – Frey is the god of fertility, warmth, and healing, the twin brother of Freya, and the father of Magnus. Frey owned a sword, Sumarbrander, which was given to Skirnir in return for his help in wooing a beautiful giantess; as a result, he is unarmed by the time of Ragnarok and will be killed by Surt. Though Magnus never meets his father until the end of the first book, he realizes that all the times his mother took him hiking through the wilderness was a way for them to get closer to Frey.
Other Norse gods
- Hel – Hel is the daughter of Loki who presides over Helheim, the realm where the unworthy dead go. One half of her is a very beautiful woman, while the other is a decaying corpse. She tries to persuade Magnus to give up Sumarbrander to Randolph, but he refuses.
- Norns – The Norns are a trio of female figures who can see the past, present, and future. They recite a prophecy to Magnus that kickstarts his journey to stop Fenris Wolf from breaking free.
Hotel Valhalla residents and staff
The following characters live or work in Hotel Valhalla and all answer to Odin. It is their duty to prepare an army for the day of Ragnarök.
- Dede – Dede is one of Magnus' fellow new einherjar. She is the daughter of two mortals. Dede is prophesied to become a thane of Valhalla.
- Halfborn Gunderson – Halfborn Gunderson is an einherji who has lived in Hotel Valhalla since the Age of the Vikings over 1,200 years ago. He died in East Anglia protecting Ivar the Boneless. He is described as "Robinson Crusoe on steroids". Having lived for a long time, Halfborn is extremely skilled and has learned many languages. He has a PhD in German literature. He almost dies at the end of The Sword of Summer, but is revived by Magnus' power of healing.
- Helgi – Helgi is a Viking from East Gothland who is the hotel manager of Hotel Valhalla and member of the Thanes.
- Hunding – Hunding is the former King of the Saxons, the bellhop of Hotel Valhalla, and Helgi's servant. Back in the year 749 C.E., Hundling and Helgi were opponents on the battlefield. When they came to Valhalla, Helgi was made the manager. His first order was to have Hunding do all the menial labor. Hunding has been at the hotel for thousands of years and longs for his family.
- Lars Alhstrom – Lars Alhstrom is an einherji and son of Thor who comes to Hotel Valhalla alongside Magnus. He died trying to free trapped people at sea.
- Mallory Keen – Mallory Keen is an Irish einherji. She is foul-mouthed and quick to criticize someone, though T.J. explains that those are her expressions of affection. She has a love/hate relationship with Halfborn Gunderson, criticizing him as a "disgusting Swede", yet is in tears when he almost dies at the end of The Sword of Summer. The Hammer of Thor reveals that the two are dating each other.
- Thanes - The Thanes are people who have been chosen to accompany Odin to Valhalla. In this franchise, they consist of historical figures who Odin has selected. When Hotel Valhalla was established, Odin made them Hotel Valhalla's board of directors. Besides Helgi and Gunilla, among the known Thanes are:
- Crispus Attucks - Member of the Thanes. He was an escaped slave who was the first person killed during the Boston Massacre.
- Davy Crockett - Member of the Thanes. He was a frontiersman and folk hero.
- Ernie Pyle - Member of the Thanes. He was a Pulitzer Prize–winning American journalist.
- Eric Bloodaxe - Member of the Thanes. He was a Norwegian ruler.
- Erik the Red - Member of the Thanes. He was a Viking who founded the first Viking settlement in Greenland.
- James Bowie - Member of the Thanes. He was a pioneer and folk hero.
- Leif Erikson - Member of the Thanes. He was an Icelandic explorer who discovered North America.
- Lord Horatio Nelson - Member of the Thanes. He was a British flag officer in the Royal Navy.
- Lord Ottar - Member of the Thanes.
- Snorri Sturluson - Member of the Thanes. He is an Icelandic historian, poet, and politician.
- Thomas Jefferson Jr./TJ – Thomas Jefferson Jr., or TJ for short, is an einherji from the 1800s....specifically, the American Civil War. He is a son of Tyr and a runaway slave. T.J. carries a bayonet made of bone-steel as his main weapon. T.J. is the first of Magnus' floormates to befriend him. He is very energetic and likes to capture hills, which was what he originally did as a private of the 54th Massachusetts.
- X – X is a half-troll and one of Sam's more controversial choices. His skin is grey and covered with warts and welts. He is called X as his real name is unpronounceable. He died in Chicago breaking up a dog fighting ring. At the end of the book, it is revealed that X is actually Odin in disguise.
- Gunilla – Gunilla, nicknamed "Gorilla" by Magnus, is a daughter of Thor, a member of the Thanes, and the leader of the Valkyries. She is spiteful towards Sam, because Sam is a daughter of Loki. She once dated a son of Loki who turned out to be a spy of his father. When Magnus escapes Valhalla, Gunilla leads the expedition to capture him, even after he and his friends release her from the giants' imprisonment. She later sacrifices herself while fighting Surt while Magnus re-imprisons Fenris Wolf. She carries a bandoleer of ball-peen hammers.
- Margaret and Irene – Margaret and Irene are Gunilla's two valkyrie aides. Magnus does not find out their names until they have been killed by the fire giants at the end of the first book.
Other Norse beings
- Draugr – Draugr are Norse zombies, usually those of Vikings.
- Gellir – A prince of the Danes who was buried with his twelve guardians, the Berserkers in a barrow in Cape Cod. He and his berserkers always vote before they decide on something, a practice known as the Thing. His sword, Skofnung, also known as the Blood River, is designated as the bride-price for the wedding of Thrym and Sam.
- Arvid – One of Gellir's protectors.
- Dagfinn – Gellir's secretary.
- Knut – One of Gellir's protectors.
- Brunnmigi – A wolf-like creature who lives inside a well in Alfheim. A Brunnmigi was responsible for the death of Andiron, Hearth's younger brother; it was then killed by the brothers' father, Alderman, who used its fur as a container for the blood tax Hearth needs to collect as repentance.
- Eikthrymir – Eikthrymir is a stag who constantly pours water into a lake, which serves as the source of all water in the Nine Worlds. It resides in Hotel Valhalla.
- Fear – Fear is a minor God of Fear who assists the Mountain Giants. In The Hammer of Thor, it is sent to compete with Sam in a game of axe throwing under the guise of a Mountain Giant called Little Billy. Sam sees through the illusion and defeats it.
- Fenris Wolf – Fenris Wolf is the lupine son of Loki and the brother of Hel and Jormungand. He was a terror in times past and the gods could only chain him up with the help of the dwarves to stop him; even Tyr had to lose his hand against the wolf, while Blitz's father, Bilì, lost his life while checking his prison on Heather Island. During Ragnarok, Fenris Wolf is destined to kill Odin and eat the sun. He is the focal point of The Sword of Summer, as the goal of Magnus and his friends is to stop Fenris Wolf from breaking free of his prison, which needs to be rebuilt. They manage to imprison him again at the end of the book. In The Hammer of Thor, it is revealed that three wolves are the children of Fenris Wolf.
- Heidrun – Heidrun is a goat whose milk is the source of the mead that serves the gods. Like Eikthrymir, Heidrun resides in Hotel Valhalla.
- Hulder – Hulder are forest spirits who inhabit Alfheim. They look like the light elves, except that they sport cow tails. Many of them serve under important light elves, sometimes as slaves in practicality.
- Inge – Inge is a female hulder serving the residence of Alderman, Hearth's father. She is miserably submissive to Alderman, despite the fact that he frequently abuses her. She is in love with Hearth but is too shy to confess it. Her mother had once served the family before her.
- Huginn and Muninn – Odin's two ravens who act as his spies as well as representatives in giving missions to his special aides, such as Sam, when he is not around. Their names mean "thought" and "memory", respectively. Helgi specifically notes that the two do not like to give PowerPoint presentations, unlike Odin.
- Jormungand – Jormungand is the serpentine son of Loki. He is a snake who circles over Midgard and is so long he must hold his tail in his mouth to prevent destroying Midgard. He is lured by Magnus and Sam to cause a ruckus in the sea big enough to summon Ran. Even after being lured, Jormungand is still half-asleep, but Ran warns that waking him up completely would cause Ragnarok, where he is destined to kill Thor.
- Jötunn - The Jötunn (also known as Jotnar) are the Norse Giants of which there are many types. Throughout the series, Mountain Giants, Frost Giants, and Fire Giants are all encountered and referred to generally as "jotunn". While some jotunn are mortal, some are not.
- Geirrod – Geirrod is a mountain giant who owns an anti-geometry house in Jotunheim. He keeps a weapon of Thor, which is mistaken by the others for his hammer. Geirrod is killed when Magnus and his friends kick the pillars of his house down while he is drunk.
- Gjalp and Greip – Gjalp and Greip are Geirrod's two mountain giantess daughters. They are killed by Jack entering their noses.
- Harald – Harald is a Frost Giant who operates a boat in the port of Boston. He helps Magnus and Sam set a bait for Jormungand in order to summon Ran. He is easily swayed by red gold, which can bribe him to do almost anything.
- Herg and Berg – Herg and Berg are members of Tiny's bowling team. They compete with Magnus and Alex in Utgard-Loki's bowling championship.
- Surt – Surt is the king of the Fire Giants of Muspellheim. He is destined to kill Frey using Sumarbrander and burn Nine Worlds during Ragnarok. Though he manages to kill Magnus, Surt's nose is cut and does not recover by the time of his second encounter with Magnus, where he is expelled back to Muspellheim.
- Thrym – Thrym is the king of the Mountain Giants. He stole Mjolnir sometime before the events of the series and in The Hammer of Thor, makes a deal with Loki to trade it in exchange for Sam's hand in marriage and the Skofnung Blade as the mundr, or the bride-price. At the end, however, he has to face the fact that his sister, Thrynga, has been planning to usurp him as ruler of the Earth Giants, and the fact that Loki has never wanted to honor his deal and give Skofnung to him. He is killed by Vidar.
- Thrynga – Thrym's sister and his only surviving family member after Thor killed them all when he was humiliated into becoming his bride. She is manipulative and wants to take the throne of the ruler of the Earth Giants from her brother. She arranges for the wedding between Thrym and a daughter of Loki, intending to steal Mjolnir and Skofnung for herself. She is incapacitated by Magnus, then finished off by Thor.
- Tiny – Tiny is a Mountain Giant who in The Hammer of Thor offers Magnus and company support in Utgard Loki's bowling championship in exchange for taking his bag to the Utgard Lanes.
- Utgard-Loki – Utgard-Loki is a Mountain Giant and the King of Jotunheim. He is sometimes mistaken for the more famous Loki, which he hates. As an eagle, Utgard-Loki forces Magnus to retrieve an apple of Idun for him, which reverts him back to his youthful state. In the second book, he attempts to prevent Loki's escape by cryptically warning Magnus, though the latter falls into the trap, anyway.
- Lindworm – Fearsome dragon the size of an eighteen-wheeler, with leathery brown bat-wings too small for flight and only two front legs. One of them is sent by Loki to catch Magnus and his friends during a Valhalla training off-guard.
- Ljosalfar – Ljosalfar are light elves who live in the idyllic world of Alfheim. They are once connected with nature and magic, but over time, their connection vanished and now they are ordinary mortals like humans. They greatly respect Frey, their ancestral master.
- Alderman – Hearth's cold, vain, and abusive father. He prefers his other son, Andiron, over Hearth, and when the former died, he forced Hearth to collect blood tax to pay for Andiron's death, leading the latter to run away from home. He is given Andvari's cursed ring to complete the tax, which causes him to exhibit the worst of his vain nature.
- Andiron – Hearth's younger brother by one year. He was killed by a Brunnmigi while he is playing with Hearth near a well in the family estate, and his death is used by Alderman to force Hearth into paying a hefty sum of blood tax for repentance. A portrait of Andiron hangs in the family's living room.
- Sunspot and Wildflower – Two elven police officers patrolling loiterers in Alfheim.
- Nøkk – Nøkk are water spirits who play sad music through violins, sending its listeners to despair. In The Hammer of Thor, a horde of Nøkk are summoned by Alderman to attack his guests and Magnus and company.
- Ratatosk – Ratatosk is a gigantic squirrel who runs around Yggdrasil, delivering hateful messages between the eagle at the top and the titanic serpent Nidhogg below. It is also tasked to capture intruders who enter and leave Hotel Valhalla without permission. Ratatosk is able to emit sorrowful callings to people, which Magnus describes as much worse than simply being gnawed by it.
- Saehrimnir – Saehrimnir is a creature whom the Aesir and einherjar kill every night for food only for it to rematerialize the next morning. Its flesh's taste depends on what its eater wants it to taste like.
- Stanley – Stanley is an eight-legged horse whom Sam speculates is a child of Odin's steed Sleipnir. He helps Magnus and his friends go through Jotunheim to reach Geirrod's residence.
- Svartalfar - The Svartalfar are a race of Norse Dwarfs that live in Nidavellir. The dwarves, like humans, are mortals, though they cannot live in a world with sunlight, as it turns them to stone. They are a matriarchal society and generally have an appreciation for creations, naming each and every one of them.
- Andvari – Andvari, also known as "The Careful One", is a dwarf who lives in Alfheim in the form of a fish. He holds a ring that can give its wielders immense wealth, yet will inflict a curse that robs them of all of their sanity and brings out their worst aspects.
- Fjalar and Galar – Fjalar and Galar are trickster dwarves who operate a boat that leads to the prison of Fenris Wolf. Anyone who barters with them usually end up stranded on the island.
- Junior – Junior is a grumpy old dwarf who hates Blitz for shaming his father, who built Fenris Wolf's prison. He challenges him to a smithing challenge before he gives him Andskoti and jewelry for Freya. He fails because of Sam's intervention, but Blitz decides not to execute Junior. Junior is more than 500 years old.
- Nabbi – Nabbi is a bartender of a bar in Nidavellir. He is also one of the members of a jury for Blitz and Junior's smithing challenge.
- Tanngrisnir and Tanngnjostr – Tanngrisnir and Tanngnjostr, also known as Otis and Marvin, are two goats who pull Thor's carriage. They are also used as source of food and they recover the next morning after being eaten, unless their bones have been broken. Marvin is more pessimistic and angry than Otis, and likes to criticize him.
Mortals are human characters who live outside of the world of magic and gods, though some may be aware of their supernatural surroundings.
The Jackson family
- Sally Jackson – Sally is Percy's mother, initially married to Gabriel Ugliano and later to Paul Blofis. In The Lightning Thief, she works in a candy shop. When she was younger, she aspired to be a writer. She is nearly killed by the Minotaur, but is discovered to be alive in the clutches of Hades. Percy travels to the Underworld to free her. In The Titan's Curse, Percy realizes she can see through the Mist, which she admits may have attracted Poseidon to her. Sally appears in all of the first five books. The Hidden Oracle reveals that she is seven months pregnant with Percy's baby half-sister. In the film adaptation, she is played by Catherine Keener.
- Paul Blofis – Paul is Sally Jackson's boyfriend and later second husband, a high school English teacher whom Percy describes as looking like a detective from a police show. Percy and his mother eventually tell Paul the truth about the gods, and he only half believes them initially. But when Percy, Nico, and Mrs. O'Leary come unexpectedly to Sally's apartment, Paul fully believes and thinks it's "awesome!" He is a competent swordsman from stage combat training in college, and he assists in the fight to save Olympus in The Last Olympian. Percy had first referred to him as "Blowfish" and as did Poseidon when he first heard about him saying "It is a shame because I rather like blowfish."
- Gabriel (Gabe) Ugliano – Gabriel Ugliano was Percy's stepfather. He is described as a loathsome man who is rude to Percy and demanding toward Percy's mother Sally. It is implied that he was physically abusive to her. Percy later learns Gabriel's strong human stench hid Percy and his mother from detection by monsters. At the end of The Lightning Thief, Percy's mother uses the severed head of Medusa to turn Gabe to stone. Sally sold Gabe's petrified body as a poker-playing statue to the Sogo art gallery. In the film adaptation, he is played by Joe Pantoliano.
The Chase family
- Caroline, Emma, and Aubrey Chase – Randolph Chase' nuclear family consists of a wife named Caroline and two daughters, Emma and Aubrey. All of them perish in a storm while accompanying Randolph in locating Sumarbrander near the coast of Boston. Loki has since promised to Randolph to return them to him should he assists the former to break free from his imprisonment. Emma was designated as Randolph's successor as researcher of Norse artefacts. Emma and Aubrey were less than 10 years old when they died.
- Frederick Chase – Dr. Chase is Annabeth's father, a professor of military history. He first appears in The Titan's Curse. He owns a Sopwith Camel. He and his daughter have had many disagreements, which caused her to run away from home at age seven. He lives in San Francisco with his wife and two sons. In The Titan's Curse, he battles monsters on the Princess Andromeda with bullets formed from celestial bronze, and, at the end of the book, is able to mend his relationship with his daughter. Frederick also appears in the Magnus Chase & The Gods of Asgard series, where he is called by his brother, Randolph, to visit Boston and search for his long-estranged nephew, Magnus who had been missing for two years, after the death of his mother/ Fredrick and Randolph's sister Natalie.
- Mrs. Chase – Mrs. Chase is Frederick's wife and Annabeth's stepmother. She is an Asian woman and the mother of Annabeth's two half-brothers, whom Annabeth barely has a relationship with. She had a dispute over the trouble monsters caused when hunting Annabeth, and that was one of the factors that led Annabeth to run away from home at the age of 7. Though Annabeth describes her in a negative light, Percy is stunned when he actually meets Mrs. Chase, because she is kind and even wants Percy to tell Annabeth that she still has her home in San Francisco.
- Bobby and Matthew Chase - Bobby and Matthew Chase are the sons of Fredrick and Mrs. Chase and are Annabeth's younger half-brothers.
- Natalie Chase – Natalie Chase was the younger sister of Randolph and Frederick, the aunt of Annabeth and the mother of Magnus. She distanced herself from her brothers and lived with Magnus as a single mother until her death at the hands of the wolves of Fenris Wolf when Magnus was 14 years old. She liked to walk with Magnus through sunlit parks, which Magnus realizes much later is a way for them to get closer with his father, Frey.
- Randolph Chase – Randolph Chase is Magnus' and Annabeth's uncle and the older brother of Frederick and Natalie. He was a professor of history at Harvard before being expelled for theorizing on the location of the first great Norse settlement in North America. He deliberately distanced himself with from all of his family when Magnus was 6 years old. Randolph had lost his wife, Caroline, and two daughters, Emma and Aubrey, in an attempt to search for the Norse boat. Randolph is secretly in league with Loki, who wants Sumarbrander. In The Hammer of Thor, he works in freeing Loki with Skofnung Blade and is last seen falling through a hole Loki makes to escape the Asgardians.
The Valdez family
- Aunt Rosa - Aunt Rosa is Leo's aunt. She blamed Leo for causing the death of her sister, Esperanza. She turned his whole family against him and called him "El Diablo" (The Devil). She refused to take him in and sent him to a social services home, which he ran away from. In The Mark of Athena, Leo sees Nemesis as Aunt Rosa, as Nemesis takes the form of the person whom the viewer has the most hatred for.
- Esperanza Valdez – Esperanza is Leo's mother. She was a trained mechanical engineer who worked at a machine shop and as an inventor. She was killed in a fire caused by Gaea and only appears in flashbacks.
- Sammy Valdez - Sammy is Leo's great-grandfather and Hazel's former boyfriend. He is described as looking identical to Leo. He and Hazel studied in a segregated school for the colored, and Sammy defended Hazel whenever she was accused for being the daughter of a witch. Hazel received her first kiss from Sammy. However, the two separated when Hazel had to move to Alaska with her mother and never met with each other again since Hazel died shortly after. Though Hazel was led to believe that Sammy moved on quickly, a flashback she has in The Mark of Athena makes her realize that Sammy remembered her well into his old age and had made the then newborn Leo promise to meet with her in his behalf.
- Rufus – Rufus was Hazel and Sammy's schoolmate in St. Agnes Academy for Colored Children and Indians during Hazel's first life. He was the leader of bullies who called Hazel a freak for summoning cursed stones and for being the daughter of a witch, but was always stopped by Sammy before he could hurt her even further.
The McLean family
- Thomas McLean – Thomas is Tristan's and Piper's late father and grandfather, respectively. He was the one who gave Piper her name. Thomas believed in Cherokee myths, which are quite similar with Greek mythology.
- Tristan McLean – Tristan is Piper's father, a movie star. He was one of Aphrodite's lovers, but did not at that time know that she was a goddess. He was captured by Enceladus in The Lost Hero, but Piper and her friends managed to save him. At the end of The Lost Hero, he is said to be back at work, though he does not remember the events of his capture. Like Piper, he identifies as Cherokee.
- Jane - Jane is Tristan's personal assistant. Piper dislikes her for taking Tristan's already little attention to bond with his daughter away from her. Through charmspeak, Jane is controlled by Medea to lure Tristan into Mount Diablo where he is kidnapped by Enceladus, and then shooing Piper away so she could not interfere. Nevertheless, Piper manages to discover the trick and rescue her father. Afterwards, Jane is fired and replaced by Mellie the cloud nymph.
The Al Abbas family
- Ayesha Al Abbas – Ayesha was Sam's late mother who worked as a doctor. Loki was one of her patients, and their intimate relationship that resulted in Sam's birth was resented by her conservative family due to its illegitimacy. She died when Sam was a child, and her responsibility for Sam was taken by her parents.
- Jid and Bibi – Jid and Bibi are Sam's maternal grandparents. They are natives of Baghdad, Iraq and immigrated to the United States before Sam was born. Jid and Bibi took care of Sam after the death of their daughter, Ayesha. Sam mentions that the two are strict on her education and impose a night curfew on her. They do not know about Sam's current occupation as a Valkyrie until Loki tells them in the events of The Hammer of Thor, and even then, due to their mortal mind, they forget about it quickly.
- Amir – Sam's fiance. Their betrothal is by arrangement, though Sam says that she fell in love with him when she was young. Like Sam, Amir is an Arab American descendant of Ahmad ibn Fadlan and thus is related to her. He is the son of Abdel, the owner of a falafel shop that Magnus frequents. In The Hammer of Thor, Amir is shocked upon learning Sam's double life and at first disheartened when she appears to be breaking off their engagement. With his power, Magnus manages to make Amir able to break through through the mist of Ginnungagap and see the Norse world. Sam later states that the two have sorted the misunderstanding and retained their engagement.
- Barry al-Jabbar – Barry is a family friend of Sam and Amir who teaches the former piloting. In The Hammer of Thor, he escorts Magnus and company to Boston from Cape Cod and is briefly possessed by Utgard-Loki, who tells Magnus to visit him.
- Beryl Grace – Thalia and Jason Grace's mother was a television actress with whom Zeus broke his oath not to have more human children. She is the first known mortal to bear children from both the Greek and Roman aspects of a god (in this case, Zeus and Jupiter). Thalia describes her as flighty, demanding and neglectful of both her children, and she would have run away from home earlier had Jason not existed. Beryl offering Jason to Hera's patronage, however, was the last straw that led Thalia to abandon her. Her stress turned her into alcohol, and she died several years before The Lightning Thief in a car accident. Melinoe impersonates her to instill fear on Thalia in the short story "Percy Jackson and the Sword of Hades" in The Demigod Files. In The Blood of Olympus, Jason encounters her mania, who wants her son to return to her so they can be a family again, an offer which Jason rejects. She then disappears in a hiss or a sigh of relief.
- Cade and Mickey — A pair of thugs sent by Nero to rob Apollo, although Meg is able to easily drive them off. Cade is described as tall and red-haired, while Mickey is short and blond-haired.
- Emma and Liz — Sadie Kane's human friends from London. The stay with Sadie in The Throne of Fire during Babi and Nekhbet's sudden attack. Sadie describes Emma as "what an Indian daughter of the singer Elton John might look like", and Liz as a "boy-crazy redhead".
- Esther – Esther is a librarian of the Jimmy Carter Presidential Library in Atlanta. She offers Percy, Frank, and Coach Hedge a ride to the Georgia Aquarium in The Mark of Athena. Hedge describes her as having the scent of potpourri.
- Germani – The Germani are the Roman Emperor's elite bodyguards. They come from Germania and are described as tall and hulking with blond hair. Two of the Germani are known: Vincius and Garius, also known as Vince and Gary, who hail from Batavia. Their names are Latinized, as Nero cannot pronounce their original Germanic names.
- Officer Gómez – Gómez is a Bostonian police officer. He wants to capture Magnus.
- Howard Claymore – Dr. Claymore is a mortal who appears solely in The Demigod Diaries story Son of Magic, written by Rick Riordan's son Haley Riordan. He is a scholar and author with theories about death; he is approached for help by a son of Hecate called Alabaster Torrington who is fleeing the consequences of siding with Kronos in The Last Olympian. Claymore later sacrifices himself so Alabaster can use an incantation to destroy a monster who is chasing him. Hecate brings him back to life in an imitative human body so that he can live on as Alabaster's protector.
- Isabel is Piper and Leo's schoolmate in the Wilderness School. She teases Piper for never meeting with her mother and for being a Cherokee, not knowing that Piper is the daughter of Hollywood star Tristan McLean.
- Julian Ramirez-Arellano – Julian is the father of Reyna and Hylla. Julian was a former soldier in Iraq before the birth of his eldest daughter. After he had Reyna, he started getting paranoid. He thought that his daughters were going after him and he eventually became a mania. One day, he attacked Hylla, knocking her out, and Reyna took a sword and killed what was left of him. Reyna and Hylla then fled from San Juan, Puerto Rico, soon after.
- May Castellan – May is Luke's mother. Like Rachel Dare, she could see through the Mist. She went insane during a failed attempt to become the Oracle. She lives in the house where she had raised Luke, alternating between cheerful expectation that he will return home and visions of his terrible fate. In The Last Olympian, Hestia reveals to Percy that Luke's mother, May Castellan, was a mortal woman blessed with the rare ability to see through The Mist, a magic substance that keeps mortals from seeing the Gods. Because of this gift, she attempted to become the new Oracle of Delphi, but was rejected. Chiron inferred that the Spirit of Delphi rejected her because she had already given birth to a child, and the Oracle was supposed to be a virgin. She survived her encounter, but became mentally unstable, seeing small pieces of the Luke's future.
- Maurice and Eddie - Two employees of Kindness International Humane Animal Transport, encountered by Percy, Annabeth, and Grover in The Lightning Thief.
- Nancy Bobofit is Percy and Grover's schoolmate in Yancy Academy in The Lightning Thief. She is a bully who frequently torments the two boys.
- Mr. and Mrs. Faust — Ruby Kane's parents, Carter and Sadie's maternal grandparents. They live in London. The two shun the magical world and take custody of Sadie, blaming Julius Kane for Ruby's death. They raise Sadie in an apparent normalcy but do not like her father or brother. The two are possessed by the gods Nekhbet and Babi in an attempt to test Sadie's resolve when she begins to pursue the Book of Ra. Mrs. Faust, usually called "Gran" by Sadie, is described as frail with curly gray hair, and a terrible cook. "Gramps" is a large, loud former rugby player. Both have been kind to Sadie, though neither is much like their daughter Ruby, her mother.
- Maria di Angelo – Maria di Angelo is Nico and Bianca's mother, an Italian diplomat's daughter. She died when Zeus struck the hotel she was staying in with lightning in an attempt to kill Bianca and Nico. Melinoe impersonated her to scare Nico.
- Marie Levesque – Marie is Hazel's mother. She was manipulated by Gaea into helping raise Alcyoneus. She died in 1942 along with Hazel. She was sentenced to the Fields of Punishment but Hazel made a compromise with the judges so they could both be sent to the Fields of Asphodel. In The House of Hades, Hecate reveals that she was Marie's mentor, teaching her magic.
- William Dare – William Dare is Rachel's father. He is the very wealthy owner of a land development company, and he first appears in The Last Olympian. Rachel hates her father because of his job, and he supported Rachel and loved her very dearlygoing to finishing school.
- Grandma Zhang – Frank's grandmother, and Emily Zhang's mother. A harsh, strict woman, she helped Frank go through the basics of both the Chinese and Roman mythologies as well as his ancestry before he departs for Camp Jupiter. Grandma Zhang was the one who saved a plank of fire that holds Frank's lifeline, a balance to his many gifts of power from both sides of his parents. In The Son of Neptune, she helps Frank get past the Laistrygonians. It is unknown whether she survived, as a white bird flew up when the fire happened.
- Riordan, Rick (2016). The Hidden Oracle. Los Angeles: Disney-Hyperion. ISBN 9781484732748.
- "Percy Jackson and the Olympians: The Lightning Thief." Scholastic Scope 58.10 (2010): 6. MasterFILE Premier. Web.
- Shrijith, A. "The World Of Percy Jackson And The Lightning Thief." Language In India 12.3 (2012): 518–523. Communication & Mass Media Complete.
- Riordan, Rick. The Lightning Thief. Percy Jackson & the Olympians (1 ed.). Puffin. p. 375. ISBN 978-0-14-138147-3.
- Riordan, Rick (2012). The Mark of Athena. New York: Disney-Hyperion. ISBN 978-1-4231-4060-3.
- Riordan, Rick. The Battle of the Labyrinth. p. 342. ISBN 978-0-14-138291-3.
- Riordan, Rick. The Sea of Monsters (British first ed.). Puffin. p. 265. ISBN 978-0-14-138149-7.
- Riordan, Rick (2010). The Lost Hero. New York: Disney-Hyperion. ISBN 978-1-4231-1339-3.
- Riordan, Rick (1 April 2007). The Titan's Curse (First ed.). Hyperion Books. p. 312. ISBN 978-0-14-132126-4.
- Riordan, Rick (4 October 2015). "Rick Riordan: 'I've loved mythology since I was a child'". The Guardian. The Guardian. Retrieved 21 November 2016.
- Homer (1996). Shankman, Steven, ed. The Iliad of Homer. 1 (books 1-12). Translated by Pope, Alexander. Eugene, OR: Wipt and Stock Publishers. book 1.23. ISBN 9781606088074.
- Riordan, Rick (5 May 2009). The Last Olympian. Percy Jackson and the Olympians. Disney Hyperion. p. 381. ISBN 1-4231-0147-2. OCLC 299578184.
- Riordan, Rick (2013). The House of Hades. New York: Disney-Hyperion. ISBN 978-1-4231-4672-8.
- Riordan, Rick (2014). The Blood of Olympus. Los Angeles: Disney-Hyperion. ISBN 978-1-4231-4673-5.
- Riordan, Rick (2009). The Demigod Files. New York: Disney-Hyperion. ISBN 978-1-4231-2166-4.
- Riordan, Rick (2012). The Demigod Diaries. United States of America: Disney-Hyperion. pp. 181–242. ISBN 978-1-4231-6300-8.
- Knight, Mary-Jane (2009). Percy Jackson & the Olympians: The Ultimate Guide. New York: Disney-Hyperion. ISBN 978-1-4231-2171-8.
- Riordan, Rick (2011). The Throne of Fire. New York, NY: Disney-Hyperion. ISBN 978-1-4231-4056-6.
- "Exclusive first chapter: 'The Kane Chronicles, Book Two". USA Today. 13 January 2011. Retrieved 23 January 2011.
- "Disney Publishing Worldwide Releases Today The Demigod Diaries by No. 1 Best-selling Author Rick Riordan Percy Jackson and the Olympians Meets The Heroes of Olympus in This Original Short-story Collection" (Press release). Disney Consumer Products. 14 August 2012. Retrieved 23 September 2014.