List of Camp Half-Blood characters
Main characters 
Percy Jackson 
Perseus "Percy" Jackson (nicknamed Seaweed Brain by Annabeth) is a 12- 17 year-old demigod, the son of Sally Jackson and Poseidon. Strongest demigod in both series, Percy Jackson is the main character of the Percy Jackson and the Olympian Series and one of the main characters in the Heroes of Olympus Series. Percy is the protagonist and narrator of the Percy Jackson and the Olympians series. As a child of one of the "Big Three" Greek gods (Zeus, Hades, and Poseidon), Percy fulfills a major prophecy of the Oracle (who later (posesses) the body of Rachel Elizabeth Dare who has been able to see through the Mist) , which foretold that the next half-blood child of the Big Three to reach the age of sixteen would have to make a decision that would mean the destruction or preservation of Olympus.
As a child of Poseidon, he has hydrokinetic powers—the ability to mentally manipulate water and can breath under water]—which develop over the course of the series, culminating in the ability to create a small hurricane in "the Last Olympian" and The Son of Neptune. Additionally, full or partial immersion in water can heal or energize him, he is immune to water pressure, and he can see and breathe underwater at any depth. Due to Poseidon's creation of horses, Percy can also communicate with equestrian animals such as Pegasi and Hippocampi. He also has an enchanted sword called Anaklusmos (Greek for "Riptide") given to him by Chiron as a gift from Poseidon (the sword was created by Zoe Nightshade, originally as a hair pin). The sword's magic disguises it as a ballpoint pen when not in use and returns it to Percy's pocket if it becomes lost.
The main plots of the five books of the Percy Jackson and the Olympians series focus on a series of quests Percy participates in along with his friends. In The Lightning Thief, he seeks Zeus's stolen master thunderbolt. In The Sea of Monsters, he seeks the Golden Fleece. In The Titan's Curse, he seeks the goddess Artemis (who is missing) and Annabeth (who fell off a cliff when battling a manticore). In The Battle of the Labyrinth, he travels the Labyrinth, a large subterranean maze, in order to defend Camp Half-Blood from attackers, and in The Last Olympian, he helps the camp and Olympus fight against the Titan army. He functions largely as an unseen character in The Lost Hero—in fact, he is the eponymous hero—but returns as the protagonist in The Son of Neptune, in which he suffers from amnesia and becomes affiliated with Camp Jupiter, an analogous camp for adolescent demigods with Roman characteristics rather than Greek. During the course of the series, he and Annabeth Chase develop mutual romantic feelings and begin dating. In the Mark of Athena, he willingly falls to Tartarus with Annabeth.
Percy is disliked by several of the Olympian gods. Among them are Dionysus (who dislikes all demigods on principle), Athena (who is Annabeth's mother and his father's rival), Ares (who has fought him and lost when he was an unknowing accomplice of Luke in the first book), Hera (who has interfered in his quests) and Hades (who considers him an upstart). However, there are also gods who respect him such as Artemis, Apollo, Hestia, Hermes, Aphrodite, and his father Poseidon. Zeus has mixed feelings for him. Then there are those who have little to no emotion to him such as Demeter, Hephaestus, and Persephone (unOlympian godess of flowers that goes into hiding in the underworld with Hades and her mother Demeter).
Percy is described as having his father's black hair and sea green eyes. His training at Camp Half-Blood helps make him athletic. He is above average height, with an athletic build, and muscular arms. He also has a "bad boy" look to him and is unpredictable. Piper Mclean says that only Annabeth Chase can tame him. Piper also states that Percy has an unpredictable adittude and has a skater look.
Annabeth Chase 
Annabeth Chase is a 12 - 16 year-old, daughter of Athena and Fredrick Chase. Born June 16. She ran away when she was 7 years old, running into two other demigods Luke and Thalia. When Grover, the satyr, finds them he tries to lead them back to Camp Half-Blood but makes a wrong turn into a Cyclopes's lair. The Cyclops captures Luke, Thalia, and Grover. When Annabeth finds them, the Cyclops mimics her father's voice. To the Cyclops's surprise, she stabs him in the foot. Then, she freed Thalia, who takes it from there; saving Luke and Grover. When she gets to camp, Thalia holds up an army of monsters for them to get away and is turned into a pine tree. For 5 years she waits for her chance to lead a quest into the real world. She gets her chance when Percy Jackson comes along.
In the first book, Percy describes her to have curly blonde hair, like a princess, with a tan and athletic build. He says that she would look like a California girl, except her stormy gray eyes take away from the rest. She is first seen when she is feeding Percy Ambrosia pudding and is asking him about what will happen at the summer solstice.He was expecting admiration from her after he defeated the Minotaur, which was what most of the demigods have been training for .After, he sees her again when Chiron introduces them. She soon leaves. Annabeth has to introduce him to the Hermes cabin, where he is placed until he is claimed by Poseidon. She joins Percy on all his quests, saved in The Titan's Curse, when she is captured, and in The Battle of the Labyrinth, where she becomes Quest Leader, taking Percy along as her second. In The Lightning Thief Percy notices she seems to have a crush on Luke, but it disappears over the first series and is gone in The Last Olympian, as she tells Luke that although he was like a brother to her, she didn't love him. She becomes jealous of Rachel Elizabeth Dare and Calypso as she suspects Percy had a crush on them. Annabeth describes Percy as her boyfriend in The Lost Hero. In the Son of Neptune, she is the only person Percy remembers. In the Mark of Athena, she and Percy reunite, and she has her own solo quest, to follow the Mark of Athena. She frees the Athena parthenos by tricking Arachne but in the end she and Percy fall into Tartarus when her leg is caught in one of Arachne's spiderwebs.
Annabeth is considered to be very pretty, especially by Percy. Aphrodite once complimented her, saying, "Annabeth, you've grown into quite a beautiful young lady." Despite having good looks, she prides herself more on her intelligence and talent at fighting. As a daughter of Athena, Annabeth excels at anything having to do with academic studies or useful arts and crafts. One of her main weapons is her intellectual abilities, especially her strategic excellence.She is said to want to become an architect when she grows up. She is also a very powerful and experienced fighter, partially since she has been training since age seven.
She was portrayed by Alexandra Daddario in the film adaptation of The Lightning Thief.
Grover Underwood 
Grover Underwood is a friend of Percy Jackson and a satyr. In the series, satyrs are in charge of identifying demigods living in the mortal world. Grover has found four of the most powerful ones: Percy Jackson, Thalia Grace, and Nico and Bianca di Angelo, all children of the Big Three. The Big Three are the three main gods, Zeus, Hades and Poseidon. After serving as Percy's protector in The Lightning Thief, he became a searcher, a coveted job among satyrs enabling him to seek the lost god Pan. 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, and in the process falls in love with a tree nymph named Juniper. He eventually finds Pan, who peacefully dies, and eventually gains recognition from the elder satyrs for his courage in battle against the Titans where he led along Percy.
Riordan mentioned in a blog post Grover would appear briefly in The House of Hades.
Grover is described as having curly brown hair and brown eyes, white pimply skin, a brown chin beard, and brown goat legs.
In the film adaption, Grover is portrayed by Brandon T. Jackson.
Thalia Grace 
Thalia Grace is a 15 (immortal) year old demigod, a daughter of Zeus. She is the older sister of Jason Grace. She ran away from home at age Nine. Grover Underwood was assigned to watch over her and ONLY her during her journey to Camp Half-Blood, during which she met Luke Castellan and Annabeth Chase. Their party arrived at the camp with a band of monsters pursuing them; Thalia confronted the monsters, allowing Grover and the other demigods to escape to the magically protected Camp Half-Blood. The monsters overpowered her, but Zeus took 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 joined the Hunters of Artemis, a band of ageless warrior girls in service to the goddess Artemis.Thalia joined the hunters the day before her sixteenth birthday, so that she couldn'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 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. In April 2012, Paloma Kwiatkowski was cast as Thalia for the upcoming Sea of Monsters film adaptation.
Thalia Grace has a silver bracelet and when she touches it, it changes into a shield, Aegis. She carries her spear in a collapsible Mace container. The shield, Aegis, is said to have Medusa's face moulded into it and people scatter in fear at the sight of it.
Tyson is a cyclops and a son of Poseidon. While he is not a demigod, he resides with his half-brother Percy at Camp Half-blood. He first appears in The Sea of Monsters as a homeless boy. Percy and Tyson are friends, but many of the other demigods at camp taunted him for his uncouth, simple nature. After proving himself on Percy's quest for the Golden Fleece, Poseidon allows Tyson to come work in his underwater forges.Tyson was known to love riding his Hippocampi, which also saved him from dying when he was on the quest with Percy. Subsequently, he communicates with Percy chiefly through Iris's rainbow network, Iris Message. On later occasions in the Percy Jackson & the Olympians series, he leads other cyclopes from the forges in battle against Typhon.
In The Son of Neptune, Tyson is searching for Percy, and he appears in Percy's dreams. At Percy's direction, Tyson finds the harpy Ella, and the two form an unlikely romantic attachment. After reuniting with Percy, Tyson participates in the defense of Camp Jupiter. In the Mark of Athena, he, Ella the harpy, and Mrs. O' Leary (Percy's hellhound) leave Camp Jupiter for Ella's safety.
Nico di Angelo 
Nico di Angelo is a 12 year-old demigod, the only known son of Hades and the younger brother of Bianca di Angelo. Nico's Roman half-sister is Hazel Levesque, a daughter of Hades' Roman counterpart, Pluto; Nico's and Bianca's existence initially seem to prove treachery on the part of Hades, who joined Zeus and Poseidon after World War II in swearing not to father any more half-blood children. In fact, the di Angelos had been born before World War II, and were kept in the Lotus Hotel and Casino in Las Vegas, where time behaves differently and people don't age. Over 70 years passed before one of Hades's Furies, Alecto, removed them from the Lotus to Washington, D.C. Subsequently, the siblings grew up in a boarding school in Maine, Westover Hall. Unlike most demigods, he does not live at Camp Half-Blood or Camp Jupiter. Annabeth Chase also states she thinks he has a crush on her but she does not feel the same way.
After his sister Bianca died while on a quest with Percy, Nico held a grudge against him, but the two later reconciled when Nico spoke to his sister's ghost. In The Last Olympian, he convinces Percy to bathe in the River Styx, granting Percy invincibility except in one spot, like Achilles. Nico also persuades Hades to lead the armies of the dead in defense of Olympus, despite the god's longstanding grudge against the Olympians. In recognition of their service, Camp Half-Blood erects a cabin for the children of Hades. In The Son of Neptune, Nico is captured while seeking the Doors of Death, which Gaia's forces are controlling to prevent their death.
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. Because of his father's abilities, Nico has powers of geokinesis, and can manipulate earth (such as creation of fissures),he also has the power of necromancy, and can put ghosts to sleep, silence ghosts with a gesture, summon undead warriors, communicate with dead, power to destroy skeleton warriors, he can 'sense' death, and,using Umbrakinesis, travel through shadows also known as shadow travel. In The Son of Neptune, Hazel says that Nico radiates an aura of death. In The Battle of the Labyrinth, he calls himself the Ghost King.
Nico has manic dark brown eyes (like his father), messy black hair, and pale skin. He favors a brown aviator's jacket. He also had a skull ring on in The Last Olympian, The Son of Neptune and "The Mark of Athena"
Also, Rick Riordan provided Nico with two separate birth dates, January 28 and May 16 of 1924. The year provides that the pact the Big Three made was sometime in 1934 or 35, making Nico about 9 or 10 when he was placed in the Casino. This confuses many due to World War II having ended around ten years later, the end being when the Big Three made the Oath.
Luke Castellan 
Luke Castellan is a 19-23 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. Luke held a grudge against the gods after his father didn't help him when his mother took fits because she could see his future after trying to become the oracle but was driven insane in the process. After running away from home at age nine, he arrived in Camp Half-Blood with Annabeth, Thalia, and Grover. Subsequently, he stole Zeus's master thunderbolt, poisoned Thalia in her tree form in The Sea of Monsters, and kidnapped Annabeth in The Titan's Curse.
Near the end of The Battle of the Labyrinth, Luke bathed in the Styx, obtaining the curse of Achilles in order to host the spirit of Kronos. But changed back into his own self for a moment after Rachel Elizabeth Dare hit him (possessed by Kronos) with a blue plastic hair brush. Kronos used Luke's body in the war against the Olympians, but Luke redeemed himself by stabbing his left armpit (his weak spot), destroying himself and Kronos. As he died, Luke explained to Percy the sadness he felt for all the kids who ended up in his father's cabin because they were unclaimed, which inspired Camp Half-Blood's later recognition of minor gods and having the gods claim their children at 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 the Dragon, while trying to steal a golden apple from the Garden of Hesperides; a quest offered to him by Hermes, which he failed.
In the film adaption, Luke is played by Jake Abel.
Jason Grace 
Jason Grace is a 15 year-old demigod (16 in The Mark of Athena), a son of Jupiter, brother of Thalia Grace, and a protagonist of the Heroes of Olympus series. He comes from Camp Jupiter, the Roman equivalent of Greek Camp Half-Blood, where demigods born to the Olympians' Roman aspects receive their training. 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 switches him and Percy Jackson the respective leaders at their camps, and steals their memories. In the rest of the book, Jason's memories begin to return to him as he quests to rescue Hera and Piper's father. He and Piper also develope romantic feelings for each other. Eventually, Jason, Piper, and Leo meet Percy and Annabeth to discuss an alliance between the camps against Gaia's armies, as Hera had planned.
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 tried eating a stapler when he was two] . He is above average height, with an athletic build, and muscular arms. He has a tattoo burned under his forearm, with twelve straight lines like a barcode, an eagle, and the letters SPQR over the lines. The tattoo symbolizes his twelve years (made every year since he was three) spent at Camp Jupiter; the eagle is a symbol of Jupiter.
Leo Valdez 
Leo Valdez is a 15 year-old demigod, a son of Hephaestus. He befriends Jason at the "Wilderness School", although it is later revealed that everything that happened prior to the Grand Canyon museum trip was actually a trick of the mist; a supernatural force that actively attempts to hide the mythical world from mortals (and sometimes demigods) by changing how mortals perceive and remember events.. 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 a mechanic. In The Lost Hero, he discovers a secret bunker hidden in the forest near camp, which contains a magic tool belt that grants him almost anything he wants, including breath mints. He uses the bunker and tool belt to repair a bronze dragon that was previously running wild in the camp's woods, naming it Festus after his initial mispronunciation of his father's name. Leo is a joker who cannot keep his hands still, and he tends to fall quickly for girls, in 'The Mark Of Athena' it is hinted he might have feelings for Hazel Levesque.
In The Son of Neptune, 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.
Leo is described as looking like a "Latino Santa's Elf" with curly black hair, dark brown eyes, pointy ears, a cheerful face, and a mischievous smile. He is described as being short with a slim build.
Piper McLean 
Piper McLean a 15 year-old demigod, a daughter of Aphrodite. She is the girlfriend of Jason Grace. Unlike most children of Aphrodite, Piper is tomboyish, unconcerned with her appearance or fashion. Her father is Tristan McLean, a famous Cherokee actor. She has the ability to use charmspeak, a power of persuasion and a rare ability in Aphrodite's children. She has unwittingly used this power to talk people into giving her things, such as a BMW convertible, and been accused of theft in the process. At Camp Half-Blood, she refuses to give in to the bullying of her cabin's head counselor, and eventually successfully challenges her for the position. She can speak French as she is a daughter of Aphrodite and French is the language of love.
Like all children of Aphrodite, Piper is described as very beautiful. She has uneven brown hair and eyes that change color, from blue to green to brown. Piper is half-Cherokee from her father's side. She has a slim build and an average height. She had a boy who was in love with her at the "Wilderness School" who turned out to be a Ventus. The Ventus said he was expecting her and the others.
Hazel Levesque 
Hazel Levesque is a 13 year-old demigod, a daughter of Pluto at Camp Jupiter, where she is friends with Frank Zhang, who has romantic feelings for her. She grew up in New Orleans, where her mother had a gris-gris shop. Due to her heritage from Pluto, and her mother's greedy wish for all the riches under the earth, precious metals and gems would frequently come up from the ground near her when she got nervous or summoned them. However, these materials were badly cursed, and brought misfortune to anyone who took them. Hazel's mother was convinced by Gaia to take her to Alaska where Gaia tried to use Hazel's power over earth to bring forth the her eldest son,giant Alcyoneus. When Hazel's mother changed her mind about helping Gaia, Hazel buried herself and her mother by calling on the riches beneath the earth, and delaying Alcyoneus's rebirth. She died in 1942, and gave up the chance to go to Elysium to save her mother from punishment, sending them both to Asphodel instead. Her mother was Louisiana Creole, so Hazel knows a small amount of French.
Before the series began, Nico di Angelo unsuccessfully sought his sister Bianca in the underworld. Nico found his half-sister Hazel, however, and helped her escape to the world of the living and Camp Jupiter. Hazel feels protective of Nico and slightly jealous of Bianca di Angelo. She feels like she owes a lot to Nico. Hazel then journeys with Frank and Percy to free Thanatos; along the way, she tames Arion, a violent, speedy horse that eats precious metals. She had a crush on Sammy Valdez and gets him confused with Leo and finds out that Sammy is Leo's bisabuelo, meaning great grandfather.
Hazel is described as having cocoa-colored skin, cinnamon brown hair, and golden eyes.
Frank Zhang 
Frank Zhang is a 16 year-old demigod, a son of Mars at Camp Jupiter, where he is friends with Hazel Levesque whom he also has a crush on. He is Chinese Canadian, and grew up with his grandmother after his mother was 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 to 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 balanced this out by tying his life force to a piece of firewood; if the wood burns out, he will die. Juno appeared to his mother while he was a baby to warn her of this fact, as he would be crucial to defeating the Giants. She grabbed the stick and extinguished the flame when Juno disappeared. In all his life, Frank has ignited the wood twice; the first time was while he was finding his way to Camp Jupiter. It was snowing and he was cold, so he thought about the stick igniting, and it did. However, he could feel his life force draining away, even though it warmed him. He thrust it into the snow to put it out. The second time was when he, Percy and Hazel traveled to Alaska to free Thanatos.
Frank is described as having a babyish face with chubby cheeks and black hair in a military cut. He has a big frame and is stoutly built. In the Mark of Athena, Annabeth compares him to a big teddy bear.
- Zeus/Jupiter — The King of the Gods, Lord of the Sky and God of Lightning. Zeus is brother to Poseidon and Hades, uncle to Percy, Nico, and Bianca, father of Thalia, and son of Kronos. Jupiter is brother to Pluto and Neptune, father to Jason, and uncle to Hazel. His symbol of power is his Master Bolt. He is 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 down Olympus, although he indirectly aids the demigods several times on their quest, such as answering his son's prayer for aid against Enceladus. In the film adaption, Zeus is played by Sean Bean.
- Hera/Juno — The Queen of the Gods and Goddess of Marriage. Hera plays a small role in The Titan's Curse, but helps Percy and the others on their quest in The Battle of the Labyrinth. Cabin 2 at Camp Half-Blood is dedicated to her, but is perpetually empty; as the goddess of marriage, she has not given birth to any demigods. She frequently meddles in the affairs of demigods, however. As Juno in The Lost Hero, she is kidnapped by Gaia, and she contacts Jason Grace to rescue her. Previously, as Juno, she had sneaked out of Olympus and exchanged Percy and Jason to try to unite the Roman and Greek demigods, going against the wishes of Zeus in doing so. Compared to Hera, Juno is more rebellious; she states that Hera would not have disobeyed Zeus as she did. In the film adaption, 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. In The Mark of Athena, Hercules sends Jason Grace and Piper McLean to obtain Achelous' other horn. When Achelous was unwilling to give up his other horn to Hercules, Piper cuts off his other horn yet doesn't give it to Hercules. Piper uses his horn as a cornucopia at Hercules, and food comes pouring out of the mouth of the horn, burying Hercules. They fly away from Hercules' island leaving behind a mourning Achelous and an angry Hercules.
- Aeolus — The Custodian of the Four Winds. Aeolus is an unseen character in the Percy Jackson & the Olympians series. In The Last Olympian, he manipulates the winds to form a barrier around Olympus that protects it from air attacks from the Titans. This also impedes Pegasus traffic, however. In The Lost Hero, he has gone insane at attempting to fill all the requests of the gods and wants to be recognized as a major god.
- Amphitrite — The Queen of the Seas. Amphitrite is the wife of Poseidon, and a daughter of Oceanus. She is resentful of Percy, a living testament to her husband's unfaithfulness. She is described as beautiful goddess, with black hair and small horns like crab claws.
- Aphrodite/Venus — The Goddess of Love, Beauty, and Lust.Aphrodite first appears briefly in The Titan's Curse. When Percy meets her, her appearance shifts constantly, matching every girl he has ever had a crush on (including Annabeth). Aphrodite is also the last child of Ouranos. Most of Aphrodite's demigod offspring are female, such as Silena Beurguard and Piper McLean. The latter's tomboyish habits vex Aphrodite, who twice changes Piper's appearance to make her look more beautiful. In The Mark of Athena, Aphrodite and Venus are revealed to be almost identical in personality and portfolio (the only difference is that Venus is more interested in high society functions), so the goddess is not rocked by an identity crisis like the rest of the Olympians. In the film adaption, Aphrodite is played by Serinda Swan.
- Apollo — The God of the Sun, Light, Poetry, Healing, Truth, Plague, Prophecy, Music, the Arts, the Oracle and more. It is said that Zeus gave Apollo more powers than an other God because he is responsible. Apollo drives a flying red Maserati Spyder convertible that glows brightly like the sun. He appears to be about 18 or 19 years old, with sandy colored hair, sky blue eyes, and dazzling white teeth. Apollo seems flirtatious, playful and optimistic, but he can also be one of the most dangerous Gods when he wants to be. He also has the most children out of any other male God. Apollo wears Ray-Ban sunglasses and sports an iPod. Percy notes that he looks similar to Luke, but less evil and without a scar. Apollo is also described by Thalia Grace as being 'hot'. Like most other Gods, Apollo is arrogant and has a big ego,and he is described as a very annoying brother by his sister Artemis. Apollo helps Percy and his friends by flying them to Camp Half-Blood in The Titan's Curse. Apollo also mentioned that Helios and Selene faded away when the Romans didn't build their temples. In The Last Olympian, he heals Annabeth's broken arm after she was thrown into her mother's throne. At the end of the war between the Titans and the gods, he certifies Rachel Dare as the new Oracle. His Greek and Roman forms have the same name as he claims that 'perfection can't be improved'. In the film adaption, Apollo is played by Dimitri Lekkos.
- Ares/Mars — The God of War and Bloodlust. 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. He wears red wraparound sunglasses that cover his flaming eyes, a bulletproof vest, combat boots, black leather biker clothes, and a black leather duster. He is the father of Clarisse, whom he blesses in battle in The Last Olympian. He appears as Mars in The Son of Neptune after a war game in Camp Jupiter, announcing the capture of Thanatos. He then claims Frank as his son, commissioning him to lead a quest to Alaska to free Thanatos. Mars is much more forward-thinking and strategic than Ares. In the film adaption, Ares is played by Ray Winstone.
- Artemis/Diana — The Goddess of the Moon, Wild Animals, and the Hunt. Artemis is the twin sister of Apollo. Cabin 8 at Camp Half-Blood is dedicated to her, though as she is a virgin goddess without demigod children, it is unoccupied, except for the rare visits when her Hunters visit. Artemis appears to be about 12 years old, with auburn hair and silvery-yellow eyes, the color of the full moon. Artemis leads the Hunters of Artemis, a group of girls who pledge to give up love in exchange for immortality and agelessness. In The Titan's Curse, she is captured by Atlas, who forces her to hold up the sky for him. She is rescued by Percy, who holds the sky for her while she fights Atlas. Together, Artemis and Percy trick Atlas into taking back the sky. Thalia then joins her Hunters, preventing Thalia from fulfilling the Oracle's prophecy. Satyrs are also reported to be attracted to Artemis because she is "so into nature." In the film adaption, 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. Athena is as beautiful, but serious and foreboding. Like most of her demigod children, she has grey eyes. She has been alternately described as having black and blonde hair. She does not actually give birth to her children; rather, they are conceived and born in her mind, just as she herself sprung from the mind of Zeus; a child of Athena is a literal brain child. Athena considers Percy dangerous, given his potential of fulfilling the prophecy that could destroy Olympus. Percy considers her the most dangerous Olympian because of her calculating intelligence, which ensures her plans rarely fail. Her Roman form, Minerva, is much less imposing, being simply a virgin goddess of wisdom, and since the Romans take virginity quite seriously, Minerva has no children. The massive differences between Athena and Minerva render the goddess functionally insane during conflicts between the Greek and Roman demigods. Athena has a personal vendetta against Rome and Roman demigods ever since the Romans stole the Athena Parthenos statue from Athens during their original invasion of Greece, and over the centuries has sent many of her children on suicide missions to retrieve it. In the film adaption, Athena is played by Melina Kanakaredes.
- Boreas/Aquilon — The God of the North Wind. Jason, Piper, and Leo seek Boreas in his palace in The Lost Hero. Jason, Piper, and Leo meet him in his palace when they come to him for help. He has two immortal children who were Argonauts, and is the father of Khione.
- Deimos — The God of Terror. A son of Ares, Deimos only appears in the "Percy Jackson and the Stolen Chariot" story in The Demigod Files, where he torments Clarisse, a demigod daughter of Ares; Percy and Clarisse cooperate to defeat him.
- Demeter/Ceres — The Goddess of the Harvest and Agriculture. Demeter made few appearances in the Percy Jackson & the Olympians series. She and her daughter Persephone appear in The Last Olympian, where they participate in the battle against the Titans. Bacchus implies that the war between the Greek and Roman demigods has trapped her in her Roman form. In the film adaption, Demeter is played by Stefanie von Pfetten.
- Dionysus/Bacchus — The God of Wine and Madness. Dionysus is Percy's cousin and the father of Castor and Pollux. He is the director of Camp Half-Blood, a position given to him as a punishment by his father Zeus for chasing an off-limits nymph. At camp, he is known as "Mr. D." Dinoysus hates his job and has a low opinion of demigods because of Theseus's abandonment of Ariadne (whom Dionysus made into his wife) and how Jason abandoned Medea. Although he enjoys playing with the camp satyrs. In The Battle of the Labyrinth, he goes in search of minor gods to recruit against the Titans. Although he claims Percy "always manages to annoy him," he has saved the lives of Percy and his friends on several occasions. When war breaks out between the Greek and Roman demigods, Dionysus goes through an identity crisis, but is able to focus enough to force himself to remain in his Bacchus form. In the film adaption, Dionysus is played by Luke Camilleri in the first film and by Stanley Tucci in the second film.
- East River - A River God who personifies the river in New York, East River only appears in The Last Olympian where he sinks Titan ships coming to attack Olympus. He is a rival of Hudson River.
- Ganymede - The Gods' Cup-Bearer. In The Sea of Monsters, Ganymede's voice was heard advising users of the Gray Sisters' taxi service to use the "seat belt" (a black chain).
- Hades/Pluto — God of the Underworld, Riches, and Death. Although technically not an Olympian, Hades is still considered to be one of the most powerful gods as he is one of the original six gods to be born of Kronos and Rhea. He is the middle brother of Poseidon and Zeus, father of Nico, Bianca, and Hazel, uncle to Percy, Jason, and Thalia, and son of Kronos and Rhea. He is the husband of his niece Persephone. Hades is portrayed as cunning and resentful of the Olympians proper, though not specifically hostile to them. In The Last Olympian, he traps Percy, planning to hold him in an underworld prison so Nico can fulfill the great prophecy. Nico, however, helps convince Hades to join in defense of Olympus against Kronos and the Titans. After his army of the dead helps Olympus win, the Olympians reward him, his demigod children, and the minor gods with full recognition at Camp Half-Blood. In the film adaption, Hades is played by Steve Coogan and is depicted to also have a fiery winged demon form.
- Hebe — The Goddess of Youth, daughter of Zeus and Hera. Hebe is among the minor gods who allied themselves with the Titans in the Percy Jackson & the Olympians series, dissatisfied with Olympian rule. She was granted cabin 18 for her children after the war. Hebe is married to Hercules.
- Hecate — The Goddess of Magic, cousin of Apollo and Artemis. Hecate is an ally of Kronos in the Percy Jackson & the Olympians series. 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 14 at Camp Half-blood.
- Hephaestus/Vulcan — The God's Blacksmith and the God of Fire. Father of Charles Beckendorf and Leo, 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, to whom he delivers the head of Festus to be used as the figurehead for the Argo II, a war vessel for the gods to use against Gaia's forces. In the film adaption, Hephaestus is played by Conrad Coates.
- Heracles/Hercules - The greatest and strongest hero in Greek Mythology who is the son of Zeus. Heracles was mentioned a lot in the Camp Half-Blood franchise. In The Titan's Curse, Zoë Nightshade was the one who gave Heracles the ideas for several of his labors, including how to steal the Apples of the Hesperides. Percy was not pleased at the fact that Heracles never gave Zoë some of the credit for this. In The Demigod Diaries episode "Percy Jackson and the Staff of Hermes," Hercules was mentioned by Cacus who stated that Hercules was the only one to have defeated him. Hercules appears as a god in The Mark of Athena. He is tasked by Zeus to guard the Pillars of Hercules. Hercules is willing to let the demigods pass into the Mediterranean at first. But when Jason and Piper mentioned that they were ordered by Hera to stop the Giants, he becomes uncooperative and orders them to break the remaining Horn of the god Achelous. They do so, but Piper refuses to give the horn to Hercules which enrages him. Yet the demigods manage to escape his wrath where Piper used the Horn of Achelous to bury Hercules in food. They fly away from Hercules' island leaving behind a mourning Achelous and an angry Hercules.
- Hermes/Mercury — The God of Travelers, Communication, and Thieves, and the Messenger of the Gods. In the Percy Jackson & the Olympians series, Hermes helps Percy, hoping that he will be able to redeem Luke. After Luke's death in The Last Olympian, he becomes angry at Annabeth for not saving him when she had the chance. In the film adaption, Hermes is played by Dylan Neal in the first film and by Nathan Fillion in the second film.
- Hestia/Vesta — The Goddess of Hearth and Home. Hestia makes few appearances, but exemplifies quiet power when she becomes involved in the affairs of demigods and Olympians. Originally an Olympian, she sacrificed her place on Olympus to Dionysus in order to prevent a civil war. She is the title character of The Last Olympian, wherein she aids Percy in his fight against Kronos.
- 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. He is a rival of East River.
- Hypnos — The God of Sleep. Hypnos is the father of the minor god Morpheus and the demigod Clovis, who sleeps frequently.
- Iris — The Goddess of Rainbows. Iris administers a network of rainbows, used by demigods and Olympians to communicate remotely. In The Son of Neptune, she meets Frank, Percy, and Hazel at her organic co-op, Rainbow Organic Foods & Lifestyles (or "ROFL," a variant of LOL). There, she sends the demigods to Phineus to discern the location of Thanatos. Her cabin at Camp Half-Blood is cabin 14.
- Janus - The God of Gates, Doorways, Beginnings and Endings. He appears as a minor character in The Battle of the Labyrinth where he offers Annabeth a choice between two doors, which represents the situation she was in when she had to make the decision about saving Luke's soul. He has two faces, and each face seems to think the exact opposite of what the other face thinks. He is also mentioned when Percy Jackson has a dream of Daedalus. Janus makes him choose to become a murderer, which he must bear as a burden for as long as he lives.
- Khione - The Goddess of Winter and daughter of Boreas who appears in The Lost Hero. Jason, Piper, and Leo encounter her in Boreas' palace. She ends up betraying them to help Gaia in her conquest.
- Lares - The Guardian Deities who are the Guardians of Camp Jupiter. There is a red-tinted Lar with the head of a wolf who guards Camp Jupiter's unicorn herd.
- Cato - A Lar. In "The Son of Neptune," Cato was seen at a 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. Morpheus is a son of Hypnos, who appears as an ally of Kronos in The Last Olympian. He puts all mortals in Manhattan to sleep before the Titan army's invasion, and puts Grover to sleep for two months during fighting in the forest of Central Park.
- Melinoe — 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.
- Nemesis — Goddess of Revenge and Balance. Nemesis is seen in the Mark of Athena Giving Leo a fortune cookie and giving advice. Nemesis is the mother of Ethan Nakamura.
- Pan — The God of the Wild. Pan is a satyr who has been missing for over 2000 years; other 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 Spring and Queen of the Underworld. Persephone is the wife of Hades, and the daughter Demeter and Zeus. Hades only allows her to visit Demeter, her mother, in the spring and summer; during these seasons, Persephone is kinder and more beautiful. Unlike most minor gods, she sides with Olympus during the war against the Titans. Persephone appears in The Demigod Files and The Last Olympian. In the film adaption, 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 Files, where he torments Clarisse, a demigod daughter of Ares. He has the power to show people their greatest fears, but Percy and Clarisse cooperate to defeat him.
- Phorcys - A primordial sea god. In The Mark of Athena, he and his sister 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 his captivity.
- Pompona — The Roman Goddess of Plenty. Pompona dislikes demigods and allies herself with Kronos and the Titans. She becomes irritated when she is mistaken for Demeter.
- Poseidon/Neptune — The God of the Sea, Earthquakes, Storms, and Hurricanes. Poseidon is a son of Kronos, brother of Hades and Zeus, father of Percy, and uncle of Thalia, Jason, Nico, Bianca, and Hazel. In The Lightning Thief, he is suspected of having stolen Zeus's master bolt, but Percy recovers the bolt, sparing his father punishment. 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. In the film adaption, Poseidon is played by Kevin McKidd.
- Terminus — The Roman God of Boundaries. In The Son of Neptune, Terminus is portrayed as obsessive-compulsive and obsessed with order. After Polybotes upsets the order in Camp Jupiter, the normally passive Terminus helps Percy destroy him.
- Thanatos — The God of Death. Thanatos is a lieutenant of Hades who guards the Doors of Death, preventing the dead from returning to the world of the living. In The Son of Neptune, the forces of Gaia 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 Athena Parthenos. He looks exactly like Gregory Peck.
- Triton - Triton is a messenger sea god and the son of Poseidon and Amphitrite. He is depicted as a merman with two fish tails. He acts arrogant toward Percy, but respects Tyson.
- 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 - Atlas is 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. 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.
- 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.
- 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.
- Kronos/Saturn — The Lord 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, Hades, Hera, Demeter, Hestia, and Chiron; he is also the father of Poseidon, 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.
- Oceanus — The Titan of the Ocean. Oceanus is depicted as having the upper body of a muscular man with a long beard and horns, with the lower body of a serpent. He did not fight the Olympians in the Titanomachy. But 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 on why he sided with Kronos to Olympus.
- Alcyoneus - A giant whom Gaia tried to force Hazel to resurrect around World War II, Alcyoneus rose again in the The Son of Neptune. He was invincible in his new home of Alaska, where he kept Thanatos captive. Frank, Hazel, and Arion defeated him after removing him from Alaska. Like the other giants, he was created by Gaia specifically to oppose one of the Olympian gods. Alcyoneus corresponds thus with Hades/Pluto.
- Enceladus - Enceladus was the first giant to be reawakened in the Heroes of Olympus series. In The Lost Hero, he was killed by Jupiter, who threw lightning at him, and Jason, as the giants can only be killed by a god and a hero working together. He opposes Athena/Minerva.
- Ephialtes and Otis - The twin Aloadae are awakened in The Mark of Athena by Gaia. They manage to capture Nico di Angelo and were tasked by Gaia to kill all demigods of prophecy but two. They fight Jason and Percy who defeat them with the help of Bacchus. They both oppose Dionysus/Bacchus.
- Polybotes - A giant who attempted to destroy Camp Jupiter with an army of monsters. He almost succeeded, but was destroyed by Percy and Terminus. He opposes Poseidon/Neptune.
- Porphyrion - A giant awakened in The Lost Hero, Porphyrion fought Jason and his friends. Hera almost killed him, but he escaped. He opposes Zeus/Jupiter.
- Calypso - Calypso first appears in The Battle of the Labyrinth, where she nurses Percy back to health on her island. She falls in love with Percy, and is heartbroken when he leaves; thousands of years ago, she experienced this with Odysseus. She was punished thus for supporting her father, Atlas, in the Titanomachy. She is released from her punishment at Percy's wish near the end of The Last Olympian.
- 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. Likes Italian suits. In the film adaption, Charon is played by Julian Richings.
- Chiron - Chiron is a centaur, a mentor of Percy and the activities director at Camp Half-Blood. In The Lightning Thief, he first appears under the pseudonym of Mr. Brunner, a substitute teacher of Percy's. He is a son of Kronos. Chiron's horse half is that of a white stallion. In the film adaption, Chiron is played by Pierce Brosnan in the first film and by Anthony Head in the second film. Also in the film adaption, the horse half is that of a brown stallion.
- Eurytion - Eurytion is a son of Ares who works on Geryon's ranch. He dislikes Geryon and eventually rebels against him and with help of Percy he defeats him. Eurytion wields a large club and gives Annabeth a mechanical spider to help her locate Hephaestus.
- Fleecy - Fleecy is a cloud nymph who works at Iris's co-op. 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.
- Phoebe - Phoebe is one of the Hunters of Artemis, the best tracker among them. She is suspicious of boys.
- Zoë Nightshade - Zoë is the leader of the Hunters of Artemis. She is a daughter of Atlas and the sea goddess Pleione. She crafted Riptide (Percy's magic sword) which was originally a gift for Heracles. She was once one of the Hesperides, but she was disowned by her family for helping Heracles. In The Titan's Curse, she battles her father who kills her. 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 is mentioned in the short story 'Son of Magic' in the Demigod Diaries. He is the son of Hecate and 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 staying 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 daughter of Hades and the older sister of Nico. She becomes a Hunter of Artemis, who 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 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 Hannibal (Camp Jupiter's war elephant). His Olympian parent is unknown.
- Butch - Butch is a son of Iris. He first appears in The Lost Hero, where he is considered Camp Half-Blood's best equestrian after Percy.
- Castor - Castor is a son of Dionysus and the twin brother of Pollux (both of whom are named after the twins of the same name). 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, god of fire. He can also make anything like his father. Charle's grandfather is Zeus. He is described as having black hair and dark eyes. He died while trying to help Percy in The Last Olympian.
- Chris Rodriguez - A son of Hermes, 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 adaption, Chris is played by Grey Damon
- Clarisse la Rue - 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.
- 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 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.
- 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, and 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 she 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 (eagle bearer) of Camp Jupiter.
- 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, a demigod briefly mentioned in "The Titan's Curse", being instructed by Annabeth 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 twins, 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's cabin, but 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.
- Pollux - Pollux is a son of Dionysus and the twin brother of Castor (both of whom are named after the twins of the same name). He survives the war against the Titans, though his brother dies in The Battle of the Labyrinth.
- Reyna - Reyna is a daughter of Bellona and the praetor of Camp Jupiter. She is the sister of Hylla, queen of the Amazons. Before her arrival at Camp Jupiter, Reyna worked for Circe, which made her suspicious of Percy. In '"The Mark of Athena", it is stated that she has harbours romantic feelings for Jason Grace. Reyna was born in Puerto Rico. She has dark hair and eyes "as black as obsidian". She also has two automaton greyhounds named Aurum and Argentum.
- Silena Beauregard - Silena is 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, her boyfriend. Luke blackmails her into continuing as a spy, but 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 unknown God. In "The Son of Neptune," she appears where she ends up helping Terminus whenever he needed her help. She would often hide from him with one of her hiding spots being underneath Terminus' statue base.
- Octavian - Octavian is an ambitious relative of Apollo (probably quarter or eighth blood) at Camp Jupiter who reads the auguries for the camp. In "The Mark of Athena" he instigates conflict between the Greeks and Romans, believing the Greeks to be in league with Gaia. He has similar features to Luke. He is also said to "look eighteen but could probably pass as younger" in The Son of Neptune in Percy's perspective.
Mythological characters 
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 gods like Ares and Artemis. Some Amazons appear in The Son of Neptune where they are sent to their compound at Reyna's request. They use Amazon.com as their business front.
- 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 Gaia 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.
- Chrysaor - Chrysaor is a human 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. Gaia was able to gather her pieces and made it so that Echo can be heard around the world. 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.
- Gaia/Terra - The embodiment of Earth, Gaia is the mother of the Titans, 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.
- 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 reached 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. In the film adaption, Tantalus is played by Mark Hamill.
- 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 Gaia, 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.
- 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.
- 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.
- Procrustes - 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.
- Theseus - 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 Gaia. He was invincible as long as he maintained contact with the ground, so Percy defeated him by hanging him in the air with chains.
- Argus - Argus is a humanoid figure with eyes all over his body who works as a security guard at Camp Half-Blood. He rarely speaks as he is said to have an eye on his tongue. He cares for Hera a lot because she is his mother.
- Arion - Arion is a horse born to Poseidon and Ceres. 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 that 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 Beckindorf 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 along with Chiron 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 along with Chiron 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.
- Keto - The most powerful sea monster in Greek Mythology and the brother of Phorcys. In The Mark of Athena, Keto appeared as a girl named Kate who is encountered in Phorcys' aquarium. When Gleeson Hodge discovered Phorcys' ruse, he freed Percy and Frank after knocking Kate out. After Percy, Gleeson, and Frank escape from the aquarium, Keto sent Skolopendra after them.
- 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 - Elephant-sized, fire-breathing bronze bulls created by Hephaestus, with horns of silver and of rubies. 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 - 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. Polyphemus is one of these. 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."
- Draco Aionius - Some of these monsters attacked Camp Half-Blood while Percy Jackson was on his adventures in the Sea of Monsters.
- Drakon - A race of giant serpent-like creatures that are several millennia older than dragons. They come in two different types: Aethiopian and Lydian. 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.
- 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.
- 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 appear in The Lost Hero. 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 the Labours 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.
- 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 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 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 adaption, 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 adaption, 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 - Aello ("storm swift"), Celaeno ("the dark") – also known as Podarge ("fleet-foot") – and Ocypete ("the swift wing") are the 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 past noon in the last day of the summer without completing their form. The Harpies also cleaned the dishes with super-hot lava and are also good in mid-town traffic. Though the harpies have been used to torture the wicked by stealing their food and not letting them sleep.
- 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.
- 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.
- Hellhounds - 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 Labryrinth.
- Hippalectryons – 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.
- Hyberboreans - A race of ice giants who freeze into ice when defeated. They side with Kronos in The Last Olympian. They can also freeze object and people using their frosty breath.
- Morrain - A Hyperborean who appeared in The Last Olympian. He was a part of a truce meeting.
- Hydra - A 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 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, centauroid creature who is half-woman, half dragon, with wings and 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 and one of them poisoned Percy. "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.
- Laistrygonians - A race of muscular cannibal giants who 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.
- Leviathan - These are mentioned by Poseidon in "The Last Olympian" as sea giants 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 - This monster has a human face and the body of a lion, as well as a scorpion's tail. A Manticore appeared in The Titan's Curse in the form of Dr. Thorn, 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 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 adaption, 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.
- Naiads - 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 - 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, 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.
- 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
- 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.
- 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.
- 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), if the crew hid below deck, Scylla would just pick up the whole boat and crush it.
- 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 - In "The Last Olympian," a sea serpent was seen amongst the sea monsters in Oceanus' army. Deimos is seen riding one in "The Stolen Chariot."
- 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 kill 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.
- 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. 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. head quarters, 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.
- Sybaris - In "The Titan's Curse," Atlas used her teeth to create spartoi.
- 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 deafeat him. He fell on some power lines thus electrocuting Bianca.
- Telekhines - 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.
- 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 King 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.
- 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.
- 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 dies of old age 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. In the film adaption, he is played by Joe Pantoliano.
- 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.
- 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. 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.
- 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 adaption, 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.
- Riordan, Rick (2010). The Lost Hero. Disney Hyperion Books. p. 553. ISBN 978-1-4231-1339-3.
- Fleming, Mike (3 April 2012). "Vancouver High Schooler Gets Dream Role In ‘Percy Jackson’ Sequel". Deadline.com.
- "'Percy' sequel zeroes in on Smith". Retrieved 2012-03-21.
- 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 (April 1, 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.
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- Riordan, Rick. The Lost Hero. Disney Hyperion Books, 2010, p. 133, 437.ISBN 978-1-4231-1339-3
- 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. The Lost Hero. Disney Hyperion Books, 2010, p. 393.ISBN 978-1-4231-1339-3
- 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. The Lost Hero. Disney Hyperion Books, 2010, p. 325, 537. ISBN 978-1-4231-1339-3
- 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