Uses her intelligence to help solve the riddles and challenges they face, particularly in...

Goddess of love and beauty, mentioned among the Olympians celebrating the heroes' success.

God of the sun, music, and healing. Mentioned as one of the Olympians pleased with the quest's...

Children of Ares led by Clarisse, known for their aggressive nature and combat skills.

Goddess of the hunt and moon mentioned when discussing the gods' return to Olympus after the...

Goddess of wisdom and warfare, mother to Annabeth and the Athena cabin children.

Restored to full strength when the Golden Fleece heals Thalia's tree, making the camp safe again.

Satyr who prepares meals for the camp, works in the dining pavilion.

Son of Apollo who runs the camp infirmary and treats injured campers.

Various nature spirits living at Camp Half-Blood, including tree nymphs and water nymphs.

Half-goat nature spirits who serve as searchers and protectors, like Grover.

One of the twin sons of Dionysus, co-head counselor of Cabin Twelve with his brother.

Wild centaurs mentioned as some of the chaotic forces unleashed when the camp's borders fail.

Head counselor of Hephaestus cabin, skilled in forging and metalwork. Creates weapons and tools for...

Proven innocent of any wrongdoing and reinstated as activities director. Returns to help restore...

Successfully completes her quest and gains respect at camp. Proves herself as a capable leader...

One of the Stoll brothers from Hermes cabin, known for pranks and mischief around camp.

Army of cyclopes working for Poseidon in his underwater forges, where Tyson goes to work.

Elder cyclopes who work in Poseidon's forges alongside Tyson. Master craftsmen of divine weapons.

Goddess of agriculture and the harvest, pleased that the Golden Fleece will help restore natural...

Tree spirits at Camp Half-Blood whose trees are dying as the magical borders fail.

Long-time camper, daughter of Athena, helps train new campers in strategy.

Successfully heals Thalia's tree and restores Camp Half-Blood's borders, even bringing Thalia back...

Rescued from Polyphemus and helps recover the Golden Fleece. His searcher skills prove valuable in...

God of fire and metalworking, father to the camp's craftsmen including those who made weapons.

God of messengers and thieves who provides magical multivitamins that protect against Circe's magic.

Veteran camper, son of Ares, follows Clarisse's lead in cabin activities.

Head counselor of Demeter cabin, skilled with plants and agriculture. Often at odds with the Stoll...

Ancient Titan lord mentioned as the ultimate enemy gathering power to return.

Head counselor of Apollo cabin, skilled archer and healer who leads his siblings in camp activities.

Appears briefly when Thalia is resurrected. Their reunion is tense as Thalia learns of his betrayal...

Son of Athena and Annabeth's second-in-command in Cabin Six. Intelligent and strategic.

Admits his mistake in firing Chiron and reinstates him as activities director. Sends Tantalus back...

Water spirits in the camp's lake and streams, also affected by the failing borders.

Nature spirits and minor deities who choose sides in the growing war between gods and Titans.

Ancient Titan mentioned as an enemy of Poseidon and his forces.

Other children of Poseidon mentioned in mythology, including both demigods and divine offspring.

Friendly centaurs led by Chiron who arrive to help defend Camp Half-Blood in the final battle.

Centaur skilled with bow and arrow who joins the defense of Camp Half-Blood.

Leader of the Party Ponies who arrives with Chiron to help defend Camp Half-Blood.

Centaur warrior wielding spears who helps fight off monsters attacking camp.

Winged horses at Camp Half-Blood that help with transportation and aerial support.

Successfully retrieves the Golden Fleece and helps restore Thalia's tree, though this also brings...

The other twin son of Dionysus, shares head counselor duties with Castor.

Takes Tyson to work in the underwater cyclopes forges, where weapons for the gods are made. Proud...

Head counselor of Aphrodite cabin, popular and beautiful camper known for her romantic advice.

Son of Demeter who cares for the camp's pegasi and other magical creatures.

Sent back to the Underworld when Chiron is proven innocent and reinstated. His cruel reign over the...

The Golden Fleece not only heals her tree but brings her back to life as a fifteen-year-old...

The other Stoll brother from Hermes cabin, partner in pranks with Connor.

Proves his worth as a hero and gains acceptance at camp. Poseidon takes him to work in the...

Son of Apollo with exceptional healing abilities, works in the camp infirmary.

Empty cabin at Camp Half-Blood dedicated to Zeus, as the Big Three gods aren't supposed to have...

A bear twin, son of Ares and an evil queen. Works for Luke aboard the Princess Andromeda.

Son of Hecate who serves Luke on the Princess Andromeda, skilled in magic and sorcery.

Student who witnesses the strange events during the dodgeball game.

Son of Apollo who teaches archery skills to campers at the shooting range.

Daughter of Athena who runs the arts and crafts activities at camp.

Bronze mechanical warriors serving Luke on the Princess Andromeda. Tireless metal soldiers.

Luke's sword made of both celestial bronze and steel, able to harm both mortals and immortals.

Confederate spirit maintaining the CSS Birmingham's steam engine and machinery.

Confederate spirit operating the CSS Birmingham's cannons under Ares' blessing.

Confederate spirit serving as lookout in the CSS Birmingham's crow's nest.

Confederate spirit who helps navigate the CSS Birmingham through supernatural waters.

A bronze dragon that attacks Camp Half-Blood when the borders fail. Breathes fire and has...

School lunch staff who serve food to students including Percy and Tyson.

Winged cleaning creatures that enforce curfew and clean up after campers.

Daughter of Athena who maintains the camp's collection of books and scrolls.

Son of Poseidon (distant relation) who teaches water activities at the lake.

Famous historical pirate transformed into a guinea pig by Circe's magic.

Ancient whirlpool monster opposite Scylla that sucks in entire ships. Creates massive underwater...

Son of Hermes who accompanies Clarisse on her quest to find the Golden Fleece. Serves as her main...

Turns Percy into a guinea pig and plans to keep him as a pet. Annabeth must rescue him using her...

Enchanted women who work at Circe's spa, most unaware they're under magical influence.

Severely damaged in battle with sea monsters but manages to reach Polyphemus's island.

Sharks with a single eye in the center of their head, distant relatives of cyclopes.

Several captured demigods held prisoner on the Princess Andromeda, forced to serve Luke's army.

Student who joins in bullying Tyson but runs when the Laistrygonians attack.

Snake-tailed women serving as crew members on the Princess Andromeda. Fierce warriors with bronze...

Daughter of Aphrodite known for her fashion sense and sometimes mean personality.

Magical electric eels that can generate powerful electrical discharges in the sea.

Vampire-like monsters disguised as cheerleaders at Meriwether Prep. Have bronze legs and donkey...

Various crew members working in the Princess Andromeda's engine room, keeping the ship running.

Son of Nemesis who has joined Luke's cause aboard the Princess Andromeda. Wears an eye patch.

The mortal ferry captain who transports passengers near the Sea of Monsters, unaware of the...

Supernatural horses that breathe fire and can run on water, encountered in the Sea of Monsters.

Son of Hermes who organizes camp competitions and games under Tantalus.

Massive sea monster with enormous tentacles that attacks ships in the Sea of Monsters.

Three ancient sisters who share one eye and one tooth, mentioned as part of the mythological world.

Men transformed into guinea pigs by Circe's magic. Former pirates and sailors who visited her...

Dark cabin dedicated to Hades, also empty due to the Big Three oath.

Cabin for children of Hecate, goddess of magic, known for their sorcerous abilities.

Various children of Hermes and unclaimed campers living in the overcrowded Cabin Eleven.

Sea creatures with horse heads and fish tails that serve Poseidon. Can communicate with Percy...

Defeated when its heads are cauterized with fire to prevent regeneration.

Another girl at Circe's spa, sister to Reyna. Also seems more aware than the other enchanted...

Goddess of the rainbow who runs the Iris-message service for communication across distances.

Spiritual operators who help facilitate Iris messages across long distances.

Son of Hephaestus who works in the forges alongside Beckendorf.

School custodian who cleans up after the supernatural incidents at Meriwether Prep.

Ancient hero who originally sought the Golden Fleece with his crew of Argonauts.

Another Laistrygonian giant disguised as a student who attacks Percy and Tyson during dodgeball.

Fellow student at Meriwether Prep who tries to be friendly with Tyson.

Cannibal giants serving as crew members aboard the Princess Andromeda.

Giant cannibals disguised as students at Meriwether Prep who attack Percy during dodgeball....

Magical leeches used by Circe in her spa treatments. Part of her enchantments to make visitors...

Student library assistant at Meriwether Prep who helps Percy with research.

New camper this summer, daughter of Demeter, still learning about camp life.

New camper who arrived just before Percy, son of Hermes.

The third Laistrygonian giant attacking Percy at school. Breathes fire like his brothers.

Revealed to be a Laistrygonian giant in disguise during the dodgeball attack.

Ancient sorceress mentioned in connection to Circe and the Golden Fleece myth.

Hotel employee who helps check in the traveling heroes in Miami.

Mortal taxi driver in Miami who unknowingly helps transport demigods.

Son of Apollo known for his archery skills and competitive nature in camp games.

Son of Aphrodite in Silena's cabin, interested in beauty and camp social dynamics.

Contemporary business executive transformed into a guinea pig after visiting the spa.

English teacher at Meriwether Prep who assigns Percy difficult reading assignments.

Percy's PE teacher at Meriwether Prep who supervises the fateful dodgeball game.

Math teacher at Meriwether Prep who notices Percy's attention problems.

Cabin for children of Nemesis, goddess of revenge, known for seeking balance and justice.

Legendary Greek hero mentioned in connection to Polyphemus. The cyclops still remembers being...

The other bear twin, brother to Agrius. Also serves Luke on the Princess Andromeda.

Blinded by Percy using a burning stick, just as Odysseus did in the ancient myths. This allows the...

Luke's cruise ship that serves as his mobile headquarters. Filled with monsters and rogue demigods.

Principal of Meriwether College Prep who deals with Percy's disciplinary issues and unusual...

Helps Percy navigate the dangerous waters of the Sea of Monsters. Shows loyalty and bravery in...

A girl working at Circe's spa who seems different from the other attendants. Has a mysterious...

Percy's celestial bronze sword disguised as a ballpoint pen. Effective against monsters.

Daughter of Ares who supervises the lava rock climbing wall.

Young new camper, daughter of Apollo, talented with archery.

Bus driver who takes students to and from Meriwether Prep, notices strange incidents.

Medical staff member who tends to injuries from bullying and the unusual incidents.

Security officer who investigates the gym damage after the Laistrygonian attack.

Attacks ships passing through her strait in the Sea of Monsters. Forces difficult choices on...

Ocean spirits who sometimes help or hinder travelers in the Sea of Monsters.

Various sea monsters that attack ships in the Sea of Monsters. Ancient creatures of the deep.

Mortal crew member who prepares meals on the Princess Andromeda, unaware of the ship's true purpose.

Show Annabeth her greatest desire - redesigning the world with perfect architecture - to tempt her...

Reanimated skeletal warriors serving as crew members on Luke's ship.

Various visitors to Circe's spa who have been transformed into animals or made compliant.

Historical Spanish explorer transformed into a guinea pig by Circe.

Various campers who work in the camp's strawberry fields as part of their duties.

Metallic birds with bronze beaks and sharp feathers that attack Camp Half-Blood when the borders...

Son of Ares who teaches sword combat techniques to campers.

Legendary crew of heroes who sailed with Jason to retrieve the Golden Fleece in ancient times.

Mortal tourists on the ferry who cannot see through the Mist to perceive the true dangers around...

Ancient Viking transformed into a guinea pig, retains some fighting spirit even in animal form.

Beach safety officer who witnesses strange supernatural events but dismisses them.