List of Camp Half-Blood characters
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- 1 Main characters
- 2 Greek/Roman Gods
- 3 Primordial Deities
- 4 Titans
- 5 Giants
- 6 Immortals
- 7 Demigods
- 8 Mythological characters
- 9 Creatures and monsters
- 10 Mortals
- 11 References
Perseus "Percy" Jackson is a young demigod, the son of the mortal Sally Jackson and Poseidon (Neptune). Percy is the protagonist and first-person narrator of the Percy Jackson and the Olympians series and one of the perspective characters in the Heroes of Olympus series, appearing in every book except The Lost Hero. Like other half-human demigods, he is expected to act as the Olympian gods' agent in the mortal world, taking action where ancient laws forbid direct godly intervention, usually in the form of quests. In the Percy Jackson and the Olympians series, Percy's age ranges from twelve to sixteen. His personality is described as "changeable" and hard to predict with the exception that he said to be rigidly loyal to his friends. His powers, which start small and develop as the books proceed, include controlling water, making hurricanes, breathing underwater, and talking to horses. He also becomes an accomplished swordfighter and leader.
Annabeth Chase first appears in the series as a twelve–year-old girl, and she turns seventeen during House of Hades. She is the daughter of Athena and mortal history professor Frederick Chase. Annabeth is Percy's first guide at camp.
She ran away from home at age seven, encountering two other demigods, Luke Castellan and Thalia Grace along the way. They live as runaways for a time until they were found by Grover Underwood, a satyr who had been ordered to escort Thalia back to camp. Annabeth and Percy complete several quests together, and they become a couple, although she remains attached to Luke, causing some jealousy on Percy's part; her attempts to bring Luke back into the fold are a minor theme in The Sea of Monsters through The Last Olympian. Later she is appears jealous of Rachel Elizabeth Dare because she suspects Percy of having a crush on her.
She prides herself primarily on her intelligence and talent at fighting. Alexandra Daddario, who portrayed Annabeth in the film adaptations, described Annabeth's physicality as a huge part of preparing for the action and fight scenes. In The Titan's Curse she holds up the weight of the sky. As a daughter of Athena, Annabeth excels at anything having to do with academic studies or useful arts and crafts. She repeatedly expresses a desire to become an architect. At the end of The Last Olympian, she is rewarded by being allowed to redesign the damaged city on Mount Olympus.
Grover Underwood, a satyr, becomes Percy's best friend during the first series. He is first seen in The Lightning Thief, where he is disguised as a human student at Percy's school, serving as his surreptitious protector and observer. Grover later reveals that if he completes enough protector missions, he will receive his "searcher's license" from the other satyrs, 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 joins Percy's quest to find Artemis in The Titan's Curse. He eventually finds Pan in The Battle of The Labyrinth, though the elder satyrs do not believe him when he reports having witnessed Pan's death. At the end of The Last Olympian, he is named a Lord of the Wild and given a seat on the satyrs' ruling council.
Grover is described as having curly brown hair, brown eyes, white pimply skin, a brown chin beard, and brown goat-legs, which he disguises with fake feet when necessary. His horns grow larger as the series progresses, and he must take increasingly careful measures to hide them while posing as human.
In the film adaptations, Grover is portrayed by Brandon T. Jackson.
Thalia Grace (pronounced THAH-lee-uh) is a 15 (immortal, but will die if killed in battle) -year-old demigod, a daughter of Zeus. She is the older sister of Jason Grace. She runs away from home at age nine and stays with Luke Castellan and Annabeth until they meet Grover when she is 12. The party arrives at the camp with a band of monsters pursuing them. Thalia confronts the monsters, allowing Grover and the other demigods to escape to the magically protected Camp Half-Blood. The monsters overpower her, but Zeus takes pity on her sacrifice, transforming her into a pine tree to save her from death.
Percy and his friends restore Thalia to life with the power of the Golden Fleece, and she joins them for the quest in The Titan's Curse. She soon joins the Hunters of Artemis, a band of immortal female archers in service to the goddess Artemis. Thalia joins the hunters the day before her sixteenth birthday, so that she wouldn't be the child of the prophecy. In The Last Olympian, she and the other Hunters help fight the Titan army of Kronos.
Thalia has electric-blue eyes and spiky black hair, and she wears dark makeup and punk style clothing. Annabeth considers Thalia's personality to be very close to Percy's, as she once said that Percy and Thalia could be each other's best friends or worst enemies.
Thalia Grace has a silver bracelet (which she gained during the Demigod Diaries) and when she touches it and says "Aegis!", it changes into a shield, Aegis. She carries her spear in a collapsible Mace container. The traditional shield Aegis is said to have Medusa's face moulded into it, and people scatter in fear at the sight of it. Thalia's shield does as well. Thalia is suspected to either have been named after the muse or the Grace, Thalia, both daughters of Zeus.
Nico di Angelo
Nico di Angelo is eleven when he first meets Percy in The Titan's Curse, when Percy, Thalia, Grover and Annabeth come to Nico's boarding school to bring him and his sister, Bianca di Angelo to camp. At the end of Titan's Curse it is revealed that Nico is the son of Hades. At first, it seems as though Hades must have, like Zeus and Poseidon, broken his post-World-War-II promise not to have more human children, but in fact Nico and Bianca had been born before the war and had been in Lotus Hotel and Casino, a place where time runs more slowly than normal. It is later revealed that their memories of their early lives had been washed away with water from the River Lethe.
Nico is initially shown as happy, cheerful and enthusiastic. During his first days at Camp Half-Blood, he follows Percy around and peppers him with questions, much to Percy's annoyance. He enjoys playing Mythomagic (a mythology-themed card game similar to Magic: The Gathering) and can quote the fictional statistics of gods and monsters from memory. After Nico learns of Bianca's death in The Titan's Curse, he is shown as strange, dark and gloomy, usually described as pale with shaggy black hair and a black shirt with a skull on it under an aviator jacket. He makes many other characters uncomfortable and is described as not belonging. He is ignored by the gods Hera and Pan, in different ways, while they are acknowledging other demigods and mortals. Nico initially blames Percy for the death of his sister Bianca, but the two later reconcile in The Battle of the Labyrinth when Nico contacts Bianca's ghost and she warns him against holding grudges, which she says is a fatal flaw for the children of Hades.
After learning that Bianca has been killed during The Titan's Curse, Nico runs away from Camp Half-Blood, blaming Percy for her death. It is revealed in The Battle of the Labyrinth that he has been living in the Underworld, camping next to the River Styx and learning about his powers from ghosts. In The Last Olympian it is revealed that he had lived in Hades' palace in the Underworld for at least a short while and was working for him in the hopes of learning more about his human mother, though he had a very strained relationship with his stepmother Persephone. After The Last Olympian, Nico is allowed to build a cabin at Camp Half-Blood specifically for the children of Hades, but it is not revealed how much time he spends there or where he primarily lives. In The Son of Neptune it is shown that he is a frequent visitor to New Rome, where he is known as Pluto's emissary.
Unlike most demigods, Nico was privy to the fact that there were two camps, one Greek and one Roman, before The Lost Hero. In The Son of Neptune, it is revealed that Nico had taken advantage of the imbalance between life and death to bring Hazel Levesque, a daughter of Pluto and his half-sister, back from the dead. He brings her to New Rome and arranges for her to join the legion. Hazel and Nico are shown as somewhat close and invested in each other's well-being.
Nico is shown as acting alone and behind the scenes or in a support capacity rather than officially joining or leading any quests. In The Last Olympian, he shows Percy how to use the River Styx to become nearly invincible in combat. He later stays in the Underworld to convince Hades to help the other Olympians fight the Titans, eventually succeeding and returning with an undead army to defend Manhattan. In the same book, Nico leaves New Rome to search the Underworld for clues regarding the cause of the recent imbalance between life and death. Off-screen, he is captured by monsters and sealed inside a bronze jar. Rescuing him before he can expire is a key plotline in The Mark of Athena. In The House of Hades, Nico leads the group across Italy to meet Percy and Annabeth at the Necromanteion in Epirus so that they can close the Doors of Death.
Many of the characters of the first series speculate that Nico has or had a crush on Annabeth, in part because he seems so uncomfortable around Annabeth and Percy together. During The House of Hades, he and Jason Grace must retrieve the scepter of Diocletian from the god Eros (Cupid). During their encounter, Cupid demands that Nico admit his secret in exchange for the scepter. Under pressure, he reveals that he was in love with Percy Jackson, though he chose to keep it a secret from everyone else in fear of rejection. Jason attempts to reassure Nico, but instead promises not to say anything. Rick Riordan has said that Nico's sexual orientation was not planned but rather developed "the longer [he] wrote about his character" and that he included a gay hero in his books because he taught so many gay and bisexual students whom he felt deserved representation. He has stated that because his books are for middle grades, they should not and will not contain sexual content beyond the occasional kiss but that treating sexual identity as an adults-only topic is "absurd." The Guardian describes this part of Nico's arc as "subtle and effective."
Nico has several different powers and abilities. He is able to feel when people die, which he describes as a buzzing sensation. He is also able to summon, communicate with, command, and banish ghosts, skeletal warriors and other undead. On one occasion, he raises a wall of rock out of the ground to stop pursuers. He can enter a death trance, which allows him to survive in stasis, by eating magical pomegranate seeds. Unlike Hazel, he is not shown as particularly connected to wealth or precious metals. He is also shown as unusually comfortable in the Underworld and knowledgeable about its geography and properties, but it is not clear whether this is supernatural or merely the result of his having lived there. Unlike most demigods, who fight with celestial bronze or Imperial gold weapons, Nico wields a Stygian iron sword capable of killing monsters and absorbing their essence.
Luke Castellan is a 19-year-old demigod, the son of Hermes and May Castellan. Introduced as the friendly head counselor of the Hermes cabin in The Lightning Thief, he is soon revealed as an antagonist and a servant of Kronos. At the end of "The Lightning Thief", Luke gets a new weapon; a sword called "Backbiter" that is half Celestial bronze and half steel, able to harm both mortals and demigods alike. Luke holds a grudge against the gods after his father doesn't help him when his mother has fits from being driven insane from seeing the future. After running away from home at age nine, he travels around the country with Thalia and then, eventually, Annabeth. It is hinted in The Demigod Diaries that he and Thalia were in a romantic relationship, seen when Thalia kisses him on the cheek; he obviously cares a lot about her seeing as he added Thalia's death to list of things the gods were to pay for in The Lightning Thief, and how he pleaded for her to join Kronos' side in The Titan's Curse.
Near the end of The Battle of the Labyrinth, Luke bathes in the Styx, obtaining the curse of Achilles, in order to host the spirit of Kronos. He changes back into his own self for a moment after Rachel Elizabeth Dare hits him with a hairbrush while he is possessed by Kronos. He allows Kronos to use his body in the war against the Olympians, but redeems himself by stabbing his Achilles spot (his weak spot) near his armpit on his left arm, destroying himself and Kronos. He turns out to be the hero of the prophecy because of his sacrifice. As he dies, Luke explains to Percy the sadness he feels for all the kids who end up in his father's cabin because they are unclaimed, which inspires Percy's requests from the gods, which are for Camp Half-Blood to recognize the minor gods and the gods' duty of having to claim their children by the age of thirteen.
Luke is described as handsome, with sandy hair, blue eyes (gold when possessed by Kronos), and a long scar on his cheek given to him by Ladon while trying to steal a golden apple from the Garden of Hesperides; a quest offered to him by Hermes, God of Travelers and Thieves, which he failed.
In the film adaptations, Luke is played by Jake Abel.
He thinks of Annabeth as a little sister that he takes care of more than a girlfriend. He obviously cares about both Annabeth and Thalia and feels like he is responsible for them.
Jason Grace is a son of Jupiter, younger brother of Thalia Grace and a perspective character in the Heroes of Olympus series. He grew up at from Camp Jupiter, the Roman equivalent of Greek Camp Half-Blood, where demigods born to the Olympians' Roman aspects receive their training. By the age of fifteen, he had earned the rank of praetor and led the legion with his longtime quest partner, Rayna. Unbeknownst to the people in Camp Half-Blood, Jason led Camp Jupiter in a concurrent war against the Titans. While Percy led the defense of Olympus in Manhattan, Jason led an assault against Mount Othrys, a Titan stronghold near San Francisco.
In The Lost Hero, Hera (Juno) kidnaps both Percy Jackson and Jason Grace, removes most of their memories, and leaves each where they will find or be found by their opposite camps. Hera hopes that this "exchange of leaders" will help the camps form an alliance and defeat the giants. In the rest of the book, Jason's memories begin to return to him as he undergoes quests to rescue Hera and Piper's father. He and Piper also develop romantic feelings for each other. Eventually Jason, Piper, and Leo meet Percy and Annabeth to discuss an alliance between the camps against Gaea's armies, as Hera had planned.
Jason's primary romantic interest is Piper McClean, but his earlier adventures with Rayna, which are not shown, are a major part of his life. Although he and Rayna were not expressly in a romantic relationship, they had completed quests together and made plans for future adventures. Similarly, his best friend in the books is Leo Valdez, but he refers to earlier friendships with Romans Dakota, Gwen and Hazel. Jason expresses some guilt at leaving Rayna to run the legion on her own and for disappointing her other hopes.
Jason has few memories of his mother, who was compelled to give him up when he was four, but he remembers enough about Thalia to not be surprised when he sees her again. Thalia reveals that their mother had told her that Jason was dead, and that this precipitated her running away from home.
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 McClean (Greek) describes Jason as very rule- and duty-oriented, completing his chores without what would be a teenager's usual complaints, but the Roman god Terminus describes him as a "rule-flouter." During The House of Hades it is revealed that Jason has plans to return to Camp Jupiter to improve it with a mental list of things that he learned at Camp Half-Blood, such as giving the fauns more rights and responsibilities, like the satyrs at Camp Half-Blood. However, when Rayna 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 son of Zeus, and is later unable to command a legion of ghosts that will otherwise obey Roman officers.
Although Jason and Percy immediately recognize that it is best to work together, their relationship is not without antagonism. As Percy puts it, it is natural for two powerful demigods to wonder which of them is stronger.
Jason is described as having cropped golden-blond hair, blue eyes, and a scar above his upper lip (according to Thalia, his older sister, he has tried eating 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 ten straight lines like a bar code, an eagle, and the letters SPQR over the lines. The tattoo symbolizes his ten years of service in the legion at Camp Jupiter; the eagle is a symbol of Jupiter.
Jason is a swordfighter like Percy, though they have different fighting styles. Jason has some power over air currents and can almost fly "like a blond Superman." He can sense and control some air spirits and has, like Thalia, called down lightning. On one occasion, he and Percy together summon a hurricane in Charleston harbor, though both are very tired afterward.
Leo Valdez is a 15-year-old demigod, a son of Hephaestus. Leo is described as looking like a "Latino Santa's Elf" with curly black hair, dark brown eyes, a cheerful face, with a slim build and a mischievous smile. He befriends Jason at the "Wilderness School", although it is later revealed that everything that happened prior to the Grand Canyon museum trip is actually a trick of the Mist. Leo also has the ability to touch and produce fire, a skill that no son of Hephaestus has had in 400 years. He is also an excellent mechanic due to his father's abilities and has experience working with machines, as his mother was also a mechanic. He repairs a bronze dragon that was previously running wild in the camp's woods, naming it Festus. He also creates the Argo II, a ship to sail the seven for the quest to Greece.
Leo tends to fall quickly for girls. In The Mark Of Athena it is hinted he might have feelings for Hazel Levesque, although in The House of Hades he falls in love with Calypso during his stay in Ogygia.
In The Mark of Athena, Hazel Levesque discovers that Leo resembles her former boyfriend, Sammy Valdez. She suspects Sammy may be an ancestor of Leo's, which is discovered to be true; Hazel and Leo figure out that Sammy Valdez is Leo's great-grandfather in The Mark of Athena.
Piper McLean is a daughter of Aphrodite. She is fifteen when she first appears, in The Lost Hero. Unlike most children of Aphrodite, Piper is tomboyish, unconcerned with her appearance or fashion. Her father is Tristan McLean, a famous actor. She has the ability to use "charmspeak," a power of persuasion found in some of in Aphrodite's children. She has unwittingly used this power to talk people into giving her things, such as a BMW convertible, which led to her being misdiagnosed as a kleptomaniac.
Piper's relationship with her father is mutually affectionate but strained, in part because of the small amount of time and attention he spares for her. The giants kidnap him during The Lost Hero and attempt to blackmail her into betraying Jason and Leo, but they are able to rescue him.
Her primary love interest is Jason Grace, though the gods Zethes and Achelous also both take an unwelcome interest in her.
After her first quest, she confronts her cabin's vain and cruel head counselor, Drew, and successfully challenged her for the position, to the relief of her half-brothers and half-sisters.
Piper is half-Cherokee on her father's side. She is described as having uneven caramel-colored hair and eyes that change color.She has a slim build and an average height.
Piper's powers include charmspeak, in which she becomes more versatile as the books proceed, and an innate ability to speak French. She can also see things that are happening far away in her knife, Katoptris. After being captured by pirates in The House of Hades, she asks Hazel to teach her swordfighting and becomes skilled.
Hazel Levesque is a thirteen-year-old demigod, a daughter of Pluto. She first appears in The Son of Neptune, at Camp Jupiter, It is later revealed that she has returned from the dead. She grew up in the 1930s and 1940s in New Orleans, where her mother had a gris-gris shop. When she was born, Pluto offered to grant her mother a wish, and she asked for great wealth, but her greed backfired into a curse. As Hazel grew older, precious metals and gems would frequently come up from the ground near her when she got nervous. However, these materials were cursed and brought misfortune to anyone who sold them. Gaea convinces Hazel's mother to take her to Alaska, over Pluto's protests, where Gaea tries to use Hazel's power over earth to resurrect her eldest son, the giant Alcyoneus, whose body is made out of precious metals and stones. When Hazel's mother changes her mind about helping Gaia, 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 Last Olympian, Nico di Angelo 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 shown as protective of each other. In The Son of Neptune, Hazel joins Frank Zhang and Percy on a quest to free Thanatos; along the way, she tames Arion, a violent, speedy horse that eats precious metals.
Hazel had a boyfriend, Sammy Valdez, in the 1940s. She later learns that Leo Valdez, who resembles him closely, is his great grandson. Hazel's primary love interest during the series is Frank Zhang. She refers to having known and been friends with Jason before his disappearance.
Several characters speculate that Pluto may be deliberately ignoring Hazel so that he will not have to order her returned to the Underworld.
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.
Hazel eventually learns to manipulate her curse, banishing cursed objects back into the earth, and sensing and moving precious metals, stones and other substances. She is an accomplished horse-rider and skilled with a spatha, a Roman cavalry sword. She is unusually knowledgeable about the Underworld because of her time there. During The House of Hades the goddess Hecate insists that Hazel learn to use magic, which in these books refers to manipulating the Mist to create and break through illusions.
Frank Zhang is a 16-year-old demigod, a son of Mars at Camp Jupiter, where he is Hazel Levesque's boyfriend. He is Chinese Canadian, and grows up with his grandmother after his mother is killed serving in the Canadian Army. Upon Percy's arrival at Camp Jupiter, Frank is the first to accept him.
Frank has a meek disposition and is uncomfortable upon learning his father's identity. He suspected himself a son of Apollo, given his skill with a bow and arrow, his preferred weapon. On his quest in The Son of Neptune, however, he uses an enchanted spear given to him by Mars when threatened by basilisks. To Frank's surprise, the spear summons a skeleton warrior that defeats the basilisks. Frank is a descendant of Periclymenus, a grandson of Poseidon, meaning he is a relative to Percy, with 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 tapped into this power and transformed into an elephant, after dragging Alcyoneus across the state line to Canada where he could be killed. However, his combined power of being a son of Mars and having the ability to shapeshift gives him too much power. The Fates balance this out by tying his life force to a piece of firewood; if the wood burns out, he will die (this is probably a reference to the ancient Greek legend of Meleager). Juno appears to his mother while he is a baby to warn her of this fact, as he would be crucial to defeating the Giants. She grabs the stick and extinguishes the flame when Juno disappears. In all his life, Frank has ignited the wood twice; the first time is while he is finding his way to Camp Jupiter. It is snowing and he is cold, so he thinks about the stick igniting, and it does. However, he can feel his life force draining away, even though it warms him. He thrusts it into the snow to put it out. The second time is when he, Percy, and Hazel travel to Alaska to free Thanatos.
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 Mars to defeat a hoard of enemies, he transforms. He is then described as being taller, more muscular and loses all his childhood fat.
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.
Reyna Avila Ramírez-Arellano
Reyna Avila Ramírez-Arellano is 16 years old. She is a demigod daughter of Bellona at Camp Jupiter, she's the younger sister of Hylla, the Amazon Queen. She has black hair and black eyes. She's a Praetor at Camp Jupiter, which she leads alone during the disappearance of Jason. She was born in Puerto Rico and worked for Circe during the first series with her sister. Reyna is often accompanied by her Pegasus Scipio 'Skippy' and her Automaton dogs, Aurum and Argentum (Gold and Silver), who can sense if someone is lying and will attack. In the end of The House of Hades, Scipio dies after extreme exhaustion and fatal poison, much to Reyna's dismay and sadness.
- Zeus/Jupiter – The King of the Gods, Zeus is most prominent in The Lightning Thief but has only small roles in the rest of Percy Jackson & the Olympians. In The Lost Hero, under the influence of Khione, Zeus forbids contact between gods and mortals and closes off Olympus, although he indirectly helps the protagonists several times on their quests, such as answering his Jason's prayer for aid against Enceladus. In the film adaptation, Zeus is played by Sean Bean.
- Hera/Juno – 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. In the film adaptation, Hera is played by Erica Cerra.
- 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.
- Akhlys – The Goddess of Misery and a daughter of Chaos and Night.
- Amphitrite – 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.
- 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.
- Notus/Auster – The god of the south wind. He appears in The House of Hades.
- Zyphyrus/Favonius – The god of the west wind. He appears in The House of Hades.
- Aphrodite/Venus – The goddess of love. Aphrodite first appears briefly in The Titan's Curse. Her appearance shifts constantly, always becoming more beautiful. In the film adaptation of The Lightning Thief, Aphrodite is played by Serinda Swan.
- Apollo – The god of the sun, light, music, and healing. Apollo drives a flying red Maserati Spyder convertible across the sky, always west. He appears to be about 17 or 18 years old with sandy-colored hair, sky-blue eyes, and dazzling white teeth. In the film adaptation of The Lightning Thief, Apollo is played by Dimitri Lekkos.
- Ares/Mars – The god of war, and father of Clarisse La Rue and Frank Zhang (as Mars). 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. In the film adaptation of The Lightning Thief, Ares is played by Ray Winstone.
- Artemis – The goddess of the moon and hunting. Artemis is the twin sister of Apollo. She has demigod children but recruits Hunters who serve as her companions and attendants. In the film adaptation of The Lightning Thief, Artemis is played by Ona Grauer.
- Athena/Minerva – The Goddess of Wisdom and Battle Strategy. 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. Her color scheme is grey. In the film adaptation, Athena is played by Melina Kanakaredes.
- 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 cooperate to defeat him.
- Delphin – 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.
- Demeter/Ceres – The goddess of agriculture. 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. In the film adaptation of The Lightning Thief, Demeter is played by Stefanie von Pfetten.
- Dionysus/Bacchus – The god of wine and parties. Dionysus was made the head of Camp Half-Blood as punishment for pursuing "an off-limits wood nymph" romantically. He has two demigod sons in-series, Castor and Pollux. Dionysus hates his job and has a low opinion of demigods because of Theseus's abandonment of Ariadne. Dionysus is played by Luke Camilleri in the first film and by Stanley Tucci in the second.
- 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 Poseidon. He is a rival of Hudson River.
- 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.
- Eros/Cupid – The god of love, 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.
- Ganymede – The gods' cup-bearer. He appears only in the film version of The Sea of Monsters, in a public service announcement advising users of the Gray Sisters' taxi service to use the seat belt.
- Hades/Pluto – 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. He is the father of Nico, Bianca, and Hazel. 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.
- Hebe – The goddess of youth and the daughter of Zeus and Hera. Hebe is among the minor gods who allied themselves with the Titans in the Percy Jackson and the Olympians series.
- Hecate – The titan-goddess of magic. Hecate is an ally of Kronos in the Percy Jackson and the Olympians series but switches sides by Heroes of Olympus. 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.
- Hephaestus/Vulcan – 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.
- Heracles/Hercules – 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 as a god in The Mark of Athena, tasked by Zeus to guard the Pillars of Hercules and issues Piper and Jason a quest for permission to enter the Mediterranean Sea.
- Hermes/Mercury – The god of messengers, travelers, and thieves. 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, 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.
- Hestia – The Goddess of hearth and home. 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 girl with a soft voice. In Percy Jackson's Greek Gods, Percy speculates that she may have helped Prometheus give fire to humans out of kindness. She does not mind being overlooked.
- 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 Poseidon. He is a rival of East River.
- 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. 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.
- 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.
- Lares – Household gods, 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. 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; 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 – The goddess of victory. She s an unseen character, but appears as a human-size figurine on the Athena Parthenos statue. She has Cabin 17 at Camp Half-Blood.
- Nemesis – The Goddess of Revenge and Balance and mother of the late Ethan Nakamura. Nemesis is seen in The Mark of Athena, where she makes a deal with Leo.
- Pan – The late god of the Wild. Pan has been missing for over 2000 years. 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, and Annabeth.
- Persephone – 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.
- 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. He has the power to show people their greatest fears, but Percy and Clarisse cooperate to defeat him.
- 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.
- Poseidon – The god of the sea, earthquakes, and horses. In The Lightning Thief, he is suspected of having stolen Zeus's master bolt but is proven innocent after Percy recovers it. 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. In the film adaptation of The Lightning Thief, Poseidon is played by Kevin McKidd. Though he is referred to as Neptune in later books, he has yet to appear in Roman form.
- 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.
- 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.
- Triptolemus – The god of farming, associated with Demeter. In The House of Hades, he protected Hazel, Frank, and Nico from the Katoblepones.
- 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.
- Gaea/Terra – The embodiment of Earth. Gaea is the mother of the Titans, the Giants, and Antaeus. She is the grandmother of the Olympians, whose rule she resents. She is the primary antagonist of the Heroes of Olympus series. 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.
- Ceto – A Primordial Sea God in Greek Mythology and the sister of Phorcys. In The Mark of Athena, Ceto 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, Ceto sent Skolopendra after them.
- Geras – The primordial 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.
- Nyx – The primordial Goddess of Night who resides at the Mansion of Night in Tartarus during the day. In The House of Hades, Percy and Annabeth have to pass Nyx's territory in which they tricked Nyx into believing that they were tourists and had a brochure that did not mention her. In her rage, Nyx showed them how important she was and summoned her children. They darkened the abyss to such an extent that Nyx herself could see anything. Nyx is described by Annabeth to be "as tall as the Athena Parthenos, but very much alive."
- Ourea – The Ourea are the primordial Gods of the Mountains who are the children of Gaea. In The House of Hades, there were some Ourea that make up the Apennine Mountains. When the Argo II tried to cross the Apennine Mountains, the Ourea there attacked them with boulders due to them being loyal to Gaea. 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.
- Phorcys – A primordial Sea God and the brother of Ceto. In The Mark of Athena, he and Ceto 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 Gaea, Tartarus fathered Typhon and the Giants. In The House of Hades, the personification of Tartarus appeared in physical form where he makes a remake about Gaea's awakening. Percy and Annabeth fought Tartarus until Iapetus and Damasen sacrificed themselves so that Percy and Annabeth can get out of the Underworld.
- Kronos/Saturn – The King of the Titans and the Titan of time and agriculture. Kronos is the main antagonist of the Percy Jackson & the Olympians series. He is the father of Zeus, Poseidon, Hades, Hera, Demeter, Hestia, Chiron and thus the grandfather of Percy, whom he tempts to join the Titan army. He fights with a scythe with a six-foot-long magical blade that can harm both gods and mortals. During the series, Kronos is initially trapped in Tartarus, but he eventually escapes to the point where he can possess Luke's body. In this form, he leads the Titan army against Olympus while Typhon occupies the Olympians' attention. On Olympus, Luke's betrayal allows Percy and Annabeth to destroy him, as Luke strikes his vulnerable part to expel Kronos' spirit from his body.
- Aigaios – The Titan of Sea Storms. 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 a Titan army) from Poseidon.
- Atlas – The general of the Titan army. He is the father of Calypso, Zoë Nightshade, and the Hesperides. Atlas was imprisoned on a mountaintop in San Francisco, forever cursed to hold up the sky. He served as the primary antagonist in The Titan's Curse, when Kronos's forces captured Artemis and forced her to take his place. Percy helps Artemis subdue him and force him back into his previous duty. In The Last Olympian, Atlas was referenced by Kronos, who decides not to free Atlas from his duty and has Krios watch over him.
- Hyperion – The Titan of Burning Light and Lord 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. The satyrs come to Percy's aid and trap Hyperion in a tree trunk. In The House of Hades, Hyperion was seen reforming in Tartarus. He and Crius are later seen guarding the Doors of Death where they allow Alcyoneus, Enceladus, Polybotes, Otis, and Ephialtes through the Doors of Death. Both of them are sucked into a vacuum that is Tartarus' face when Tartarus shows up to fight Percy and Annabeth.
- Iapetus – The Titan of mortality, pain, and death. In The Demigod Files, Percy drags Iapetus into the river Lethe, erasing the Titan's memory. Nico subsequently attempts to train Iapetus, who is told his name is Bob. In The House of Hades, Nico is training Bob to think that Iapetus had helped the Olympians in the Titanomachy. He is later very important as he sacrifices himself for Percy and Annabeth so they can get through the Doors of Death.
- Krios – The Titan of stars and the constellations, and lord of the South. Percy sees Krios in a dream where he guards Atlas. He wears armor decorated with glowing stars. In The Lost Hero, Jason claims to have defeated Krios with some luck. In "The House of Hades," Krios was seen with Hyperion guarding the Doors of Death where they allow Alcyoneus, Enceladus, Polypotes, Otis, and Ephialtes through the Doors of Death. Both of them are sucked into a vacuum that is Tartarus' face when Tartarus shows up to fight Percy and Annabeth.
- 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 Titanomachy. In The Last Olympian, he becomes convinced Kronos will be able to defeat Olympus. Oceanus joins the other Titans in the war, assaulting Poseidon's forces underwater. 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 Titanomachy, but joins the Titan army in the Percy Jackson & the Olympians series because he had a foresight that the Titans would win. Prometheus was part of the truce party that Percy Jackson was in. He flees after Kronos's defeat, sending a list of excuses to Mount Olympus to explain why he siding with Kronos.
The giants were made by Gaia and Tartarus to overthrow Olympus. Each was meant to oppose a specific god. They can only be defeated by a gods and heroes working together. They are mostly described as very tall with dragon legs and shaggy hair with different objects braided into it.
- Alcyoneus – A giant 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. Like the other giants, he was created by Gaia specifically to oppose one of the Olympian gods, in this case Hades. In The House of Hades, Alcyoneus returns to the living world through the Doors of Death.
- 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, Frank and Hazel. He opposes Hecate.
- Damasen – A peaceful giant who appears in The House of Hades. He had been exiled to Tartatus 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. He had been made to oppose Ares.
- Enceladus – Enceladus was the first giants to be reawakened in the Heroes of Olympus series. In The Lost Hero, he is killed by Jupiter, who throws lightning at him, and Jason, as the giants can only be killed by a god and a hero working together. He opposes Athena. In The House of Hades, Enceladus re-enters the world through the Doors of Death.
- Ephialtes and Otis – Ephialtes and Otis are twin giants. They are awakened in The Mark of Athena by Gaia. 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. They both oppose Dionysus. In The House of Hades, Ephialtes and Otis they return to the living world through the Doors of Death.
- Polybotes – Attempts to destroy Camp Jupiter with an army of monsters. He is killed by Percy and Terminus. He opposes Poseidon and can turn water to poison. 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 – Awakened in The Lost Hero, Porphyrion fights Jason and his friends. Hera almost kills him, but he escapes. He opposes Zeus.
- 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 imprisoned as 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.
- 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.
- 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.
- 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.
- 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.
- Lupa – Lupa is the wolf that raised Romulus and Remus. She guides the children of Roman gods to Camp Jupiter. She appears in The Lost Hero and The Son of Neptune.
- 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 and The Lost Hero.
- 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."
The following are the children of the Gods:
- 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 in 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.
- Austin – Austin is only mentioned in The Last Olympian. Though his Olympian parentage was never revealed, Apollo is a possibility seeing as how he was shooting a bow.
- 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 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.
- Bobby – Bobby is a caregiver of Camp Jupiter's war elephant Hannibal. His Olympian parent is unknown.
- Castor – Castor is a son of Dionysus and the twin brother of Pollux (both of whom are named after the Gemini). He was killed in The Battle of the Labyrinth when he was stabbed by a demigod allied with Kronos.
- Charles Beckendorf – Charles Beckendorf is the son of Hephaestus. He can also make anything like his father. Charles's grandfather is Zeus. He is described as having black hair and dark eyes. He is in a relationship with Silena Beauregard. He died while trying to help Percy in The Last Olympian.
- 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 went insane 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.
- Clarisse La Rue – A daughter of Ares and the lead counselor of the Ares cabin 5, Clarisse is hot-tempered, arrogant, large, and strong. She dislikes Percy, but she is capable of compassion, such as in her treatment of Chris. She later befriends Silena Beauregard, after Silena gives her advice on her first boyfriend. Like Achilles in the Trojan War, Clarisse initially sits out the war for Olympus due to a personal feud. Silena (echoing Patroclus) impersonates Clarisse and leads the Ares cabin into battle, but is killed. Enraged at the loss of her friend, she joins the battle with a fury reminiscent of her father's. In the film adaptation, Clarisse is portrayed by Leven Rambin.
- Clovis – Clovis is the lead counselor of the Hypnos cabin. In The Lost Hero, Annabeth consults him regarding Jason's memory loss.
- 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 survive the Titan war.
- Dakota – A son of Bacchus at Camp Jupiter, Dakota drinks Kool-Aid copiously being too young for actual wine. He is both a centurion of the Fifth Cohort and a senator. Dakota often needs help putting on his toga.
- Drew Tanaka – Drew is the lead counselor of the Aphrodite cabin, succeeding Silena, in The Lost Hero. She bullies her cabin members, leading Piper to successfully challenge her for the lead counselor position. Like Piper, she has the charmspeak ability. She is also mentioned in the Serpent's Shadow of the Kane Chronicles in Sadie's school dance, being someone Sadie hates.
- 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 stated to Percy that the minor gods should at least have thrones.
- Gwendolyn – 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 the day after and is replaced by Frank.
- 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. 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, 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.
- Katie Gardner – Katie is the head counselor for Demeter's cabin at Camp Half-Blood. She survives the war with the Titans. Katie strongly dislikes the Stoll brothers, who once put chocolate Easter bunnies on the Demeter cabin's grass roof.
- Kayla – Kayla is only seen or mentioned in The Last Olympian, where she was seen carrying orders by Michael Yew. Her Olympian parentage is unknown, though because she was shooting a bow, she might be a daughter of Apollo.
- Lacy – Lacy is a daughter of Aphrodite who befriends Piper in The Lost Hero. She also appears in The Kane Chronicles. In "The Serpent's Shadow," Ruby Kane mentions rival gods and magic to that of Egypt. As Lacy and possibly Drew appear in New York and Lacy mentions that her and Drew had gone to "some summer camp" together and she had been just as much a tyrant there, it is possible that these are the same Drew and Lacy as mentioned in The Heroes of Olympus series.
- Larry – A senator at Camp Jupiter and a member of either the First or Second Cohort.
- Laurel – Laurel was only mentioned in The Titan's Curse. Though because she was following Silena Beauregard, she may be a daughter of Aphrodite.
- Lee Fletcher – Lee was the head of Apollo cabin. He is killed by a giant in The Battle of the Labyrinth.
- Lou Ellen – Lou Ellen is a daughter of Hecate in The Lost Hero. She is known for playing magical tricks on fellow campers.
- Malcolm – Malcolm is the assistant counselor of the Athena cabin, under Annabeth.
- Michael Yew – Michael 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. Percy finds it very interesting that he's the counselor. 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.
- Mitchell – Mitchell is a son of Aphrodite who befriends Piper in The Lost Hero.
- Nyssa – Nyssa is a daughter of Hephaestus. She "befriends" Leo in The Lost Hero. She is mentioned on several occasions in the beginning and end of The Lost Hero.
- 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.
- Silena Beauregard – Silena was the head of the Aphrodite cabin for most of the Percy Jackson & the Olympians series. She served as a spy for Kronos within Camp Half-Blood, but wanted to quit when her actions led to the death of Beckendorf (who was her boyfriend). 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. They survive the Titan war.
- Will Solace – Will is the head of the Apollo cabin in the Heroes of Olympus series. In The Last Olympian, he healed Annabeth.
The following are the second or further generations of the gods:
- 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 ambitious and cunning. He describes himself a descendant of Apollo in The Son of Neptune but Rayna 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."
The following characters from Greek mythology appear in this series:
- Achilles – The ghost of Achilles appears briefly in The Last Olympian, warning Percy about the Curse of Achilles.
- 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. In the novels, they also run the billion-dollar Amazon.com, which they use as a source of cover and revenue.
- Hylla – Reyna's sister and the current Queen of the Amazons.
- 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 out Percy, who declined.
- Lulu – An Amazon guard who is loyal to Otrera. In The Son of Neptune, Lulu 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 drider-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.
- 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 Zetes is shown to be metrosexual 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.
- Cercopes – 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 Cercopes have set up shop in Balogna, Italy. When the Argo II docks there, the Cercopes 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.
- 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 fell into the sea.
- 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.
- Daedalus – Architect of the Labyrinth, Daedalus is the son of Athena and the father of Icarus. He killed his nephew Perdix upon one of the choices given to him by Janus which enabled him to cast his soul into automatons. Athena branded him with the murderer's brand. 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.
- 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.. 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.
- The Fates – The three women who control 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.
- 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.
- 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 Gaia 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. Though 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, however 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.
- 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, a mortal, 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.
- 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 – 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. When Nico was trying to summon Bianca in The Battle of the Labyrinth, he ended up summoning the spirit of Theseus.
Creatures and monsters
- Agrius and Oreius – Agrius and Oreius are humanoid bears that were a result of a union between a woman and a bear due to the power of Aphrodite. The two served as Luke's henchmen in The Sea of Monsters.
- 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.
- 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.
- 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.
- 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 cuss when his abilities are challenged.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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. 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).
- Cloud Nymph – Nymphs associated with the clouds.
- Fleecy – A Cloud Nymph who appeared in The Son of Neptune where she works at R.O.F.L.
- 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.
- Cyclops – A race of one eyed-giants who have three species as mentioned in "The Lost Hero". The first are the Elder Cyclops who are friendly and help the gods ever since the Titanomachy. Tyson is one of these. The second is the southern species who raise goats and live in caves. The third is the northern group who helped the Titans make weapons. In The Last Olympian, some rogue Cyclopes were seen fighting with Kronos' army in "The Battle of Manhattan."
- Ma Gasket – A 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.
- Polyphemus – A 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". He later tried to eat them.
- Sump – The son of Ma Gasket who appears in "The Lost Hero".
- Torque – The son of Ma Gasket who appears in "The Lost Hero."
- Tyson - Percy's half brother who first appears in "The Sea of Monsters." He first met Percy at school where Percy thought he was a normal boy because of the Mist, during a dodge ball it was shown that Tyson was fireproof. Annabeth later reveals to Percy that Tyson is a Cyclops.
- Draco Aionius – Some of these monsters attacked Camp Half-Blood while Percy Jackson was on his adventures in the "The Sea of Monsters".
- Drakon – 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 – 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. In The Last Olympian, Kronos unleashed it upon Manhattan where it killed many half-bloods before being killed by Clarisse La Rue.
- Maeonian Drakon - In the House of Hades, the Maeonian Drakon attacked Percy, Annabeth, and Bob, and was killed by Damasen.
- Dryad – Dryads are a species of nymphs that are associated with trees and forests.
- 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.
- Eidolons – A race of spirits that can possess demigods. In The Mark of Athena, the Eidolons work for Gaea.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Gegeines – A race of 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.
- 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 completed 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 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 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 that might be Python. 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.
- 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 uses her head to turn Gabe Ugliano to stone. In the film adaptation, Medusa is played 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 played by Mary Birdsong, Yvette Nicole Brown, and Missi Pyle.
- 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.
- 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 on the side of the Titans.
- 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."
- Hekatonkheires – The Hundred-Handed Giants of incredible strength, superior even to the Cyclopes. They are taller than mountains. The last one, Briares, was imprisoned 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.
- 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.
- Hyberborean – 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.
- 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." They Hydra is ultimately defeated by the use of Medusa's head.
- 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 Camp Fish-Blood 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.
- Karpoi – The spirits of the grain who are the size of toddlers. In "The Son of Neptune," Percy Jackson, Hazel Levesque, and Frank Zhang encounter three Karpoi.
- 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.
- Ketos – Chiron mentions this giant sea monster in "The Titan's Curse".
- 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.
- 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.
- 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.
- 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.
- 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 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.
- 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.
- Naiad – 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.
- Nemean Lion – The Nemean Lion is a lion that is one of the children of Echidna and Typhon. 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.
- Ophiotaurus – A half-cow/half-snake monster. It is an ancient creature which could bring down the gods if it were slain and its entrails were sacrificed on a brazier. 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 – Bessie is the Ophiotaurus Percy meets in "The Titan's Curse." Percy named it because of its bovine appearance, but it was in fact a male. Bessie was supposedly the creature that Artemis was hunting because it could destroy Olympus. She also briefly appeared in "The Last Olympian" where Percy sees him in an aquarium.
- Pegasus – Pegasi are winged horses that are named after the original mount of Bellerophon.
- 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, Luke's demon cruise ship, 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".
- Guido – A light gray(white) Pegasus who is friends with Blackjack. In "The Last Olympian," Guido and Porkpie aided Percy and Blackjack in the Battle of Manhattan.
- Porkpie – A light gray(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).
- 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.
- 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.
- Satyr – Half man, half goat. Most of the Satyrs work at Camp Half-Blood. Their Roman counterpart is a Faun. 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. He is killed in The Last Olympian and is reincarnated as a laurel. He hates Grover and thinks he is a liar. 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" and that he has suspicions that Grover is a spy.
- 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.
- Gleeson Hedge – Percy Jackson finds a letter addressed to Grover Underwood in "The Last Olympian" where he tried to summon Pan's spirit to help fend off some giant badgers. He played a major role in The Lost Hero, posing as a football coach at a school for troubled kids. He is the protector of Leo Valdez and Piper McLean
- 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.
- 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.
- 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.
- 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 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 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 a Spartoí, 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.
- 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.
- 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."
- Sybaris – In "The Titan's Curse," Atlas used her teeth to create spartoi. In "The House of Hades," she is in the form of a kitten and is Bob the Titan's friend.
- 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.
- 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." Grace tames Tempest so that it can help him fight Porphyrion. He is shown on the cover of The Mark of Athena with Jason riding him, but it isn't official that that is actually Tempest
- 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.
- 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.
- Esperanza Valdez – Esperanza is Leo's mother. She was a Hispanic-American mechanic who received a college degree in mechanical engineering. She was killed in a fire caused by Gaea, when Mother Earth faced eight-year-old Leo Valdez.
- Emily Zhang – Emily is Frank's mother who died in Afghanistan. She loved Mars and has ancestors from Pylos. After her death, her mother raises Frank and it is unclear wether or not she esacpes when her mansion burns down in "The Son of Neptune."
- 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.
- 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.
- Mrs. Dare – Mrs. Dare is Rachel's mother, who briefly appears in The Last Olympian. She went to Clarion Ladies' Academy, a finishing school for girls in New Hampshire, and wants Rachel to go there as well. Her first name is not revealed.
- Ms. Grace – Ms. Grace is the mother of Jason and Thalia Grace. She is the first known mortal to bear children to both the Greek and Roman aspects of the same god (Zeus and Jupiter). Her first name not revealed.
- Maria di Angelo – Maria di Angelo is Nico and Bianca's mother. She died when Zeus struck the hotel she was staying in with lightning in an attempt to kill her demigod children.
- Marie Levesque – Marie is Hazel's greedy mother who was manipulated by Gaea into helping raise Alcyoneus. She died in 1942 along with Hazel. She was sentenced to Eternal Punishment but Hazel made a compromise with the judges so they could both be in the Fields of Asphodel.
- May Castellan – May is Luke's mother, who went insane after attempting to become the Oracle. She continued to make large amounts of sandwiches, burnt cookies, and Kool-Aid for Luke, hoping he would someday return home.
- Paul Blofis – Paul is Sally Jackson's boyfriend and later husband, making him Percy's stepfather. 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 an excellent 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 that "It was a shame because he rather liked blowfish"
- Rachel Elizabeth Dare – Rachel is a mortal girl who can see through the Mist, the force that obscures the true nature of 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 aids Annabeth and Percy by guiding them through the Labyrinth to Daedalus's workshop. In the same book she hit Kronos, or Luke, with her hair brush and forced Kronos and give back a short while of consciousness to Luke. It is hinted throughout the series that she harbors romantic feelings for Percy; Annabeth has noticed this and become 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 Great Prophecy about the next generation of heroes, setting the plot of the Heroes of Olympus series. In the Mark of Athena it is mentioned she is comparing prophecies with Ella, hoping to find out more to help fight against the giants. In the House of Hades she made kind of an appearance in Jason's dream vision,visiting Reyna, Octavian and other Romans in their base with Grover. She tried to persuade Reyna to go to the ancient lands and carry the Athena Parthenos to Camp Half-blood as a sign of peace.
- 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 likely attracted Poseidon to her. Percy is very close to his mother. After failing to contact Annabeth, she is the first person he calls in The Son of Neptune. In the film adaptation, she is played by Catherine Keener.
- Tristan McLean – Tristan is Piper's father, a very famous Cherokee movie star. He was one of Aphrodite's lovers, but Aphrodite never revealed who she really was, because she was afraid that Tristan would be unable to hold the information that the gods were real. 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 with assistants Mellie and Gleeson Hedge (though the latter left to chaperone for the quest against the giants in The Mark of Athena).
- William Dare – William Dare is Rachel's father. He is the very wealthy owner of a land development company in Brooklyn, and he first appears in The Last Olympian. Rachel hates her father because of his job, and he supported Rachel going to finishing school.
- "Alexandra Daddario discusses returning as Annabeth Chase Percy Jackson: Sea of Monsters". The Fan Carpet. December 3, 2013. Retrieved September 1, 2014.
- Fleming, Mike (3 April 2012). "Vancouver High Schooler Gets Dream Role In 'Percy Jackson' Sequel". Deadline.com.
- Riordan, Rick. "Frequently Asked Questions About Me: The Online World of Rick Riordan". Retrieved August 31, 2014.
- "Heroes of Olympus: The House of Hades by Rick Riordan – review". The Guardian. March 11, 2014. Retrieved August 31, 2014.
- Riordan, Rick. The Lightning Thief. Percy Jackson & the Olympians (1 ed.). Puffin. p. 375. ISBN 978-0-14-138147-3.
- Riordan, Rick. The Lost Hero. Disney Hyperion Books, 2010, p. 498.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. The Battle of the Labyrinth. p. 342. ISBN 978-0-14-138291-3.
- Riordan, Rick. The Lost Hero.
- 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 (10 February 2009). "Percy Jackson and the Stolen Chariot". The Demigod Files. Disney Hyperion. p. 160. ISBN 1-4231-2166-X.
- Riordan, Rick. The Sea of Monsters (British first ed.). Puffin. p. 265. ISBN 978-0-14-138149-7.
- Riordan, Rick (10 February 2009). "Percy Jackson and the Sword of Hades". The Demigod Files. Disney Hyperion. p. 160. ISBN 1-4231-2166-X.
- Riordan, Rick (10 February 2009). The Demigod Files. Disney Hyperion. p. 160. ISBN 1-4231-2166-X.
- Percy Jackson and The Olympians: The Ultimate Guide