| Princess |
Andromeda | Ship named after myth |
| Corey |
Bailer | Classmate |
| Silena |
Beauregard | Daughter of Aphrodite |
| Charles |
Beckendorf | Leader of Hephaestus cabin |
| Joe |
Bob | One of Sloan's friends, a giant |
| Mr. |
Bonsai | Headmaster |
| Colchis |
Bulls | Magical automata created by Hephaestus |
| Luke |
Castellan | Son of Hermes, antagonist |
| Annabeth |
Chase | Percy's friend, daughter of Athena. Aka: Wise Girl; Nobody |
| Mr. |
De Milo | English teacher |
| Scythian |
Dracaenae | Dragon women |
| Amelia |
Earhart | Historical aviator (reference) |
| Skull |
Eater | One of Sloan's friends, a giant |
| Laistrygonian |
Giants | Mythological monsters |
| Thalia |
Grace | Daughter of Zeus |
| Percy |
Jackson | Protagonist, a demigod son of Poseidon. Aka: Seaweed Brain; Perseus |
| Sally |
Jackson | Percy's mother |
| Clarisse |
La Rue | Daughter of Ares |
| Raj |
Mandali | Classmate |
| Dean |
Martin | Musician (reference) |
| Coach |
Nunley | PE teacher |
| Chris |
Rodriguez | Hermes cabin camper |
| Matt |
Sloan | Bully |
| Connor |
Stoll | Hermes cabin leader |
| Travis |
Stoll | Hermes cabin leader |
| Marrow |
Sucker | One of Sloan's friends, a giant |
| Edward |
Teach | Son of Ares. Aka: Blackbeard |
| Mrs. |
Tesla | Science teacher |
| Grover |
Underwood | Percy's best friend, a satyr |
| Agrius |
| Twin, Luke's assistant |
| Aethiopian Drakon |
| Dragon in cargo hold |
| Anger |
| One of the Gray Sisters |
| Apollo |
| God of archery |
| Ares |
| God of war |
| Argus |
| Former camp guard |
| Artemis |
| Goddess of the hunt |
| Atalanta |
| Female hero |
| Athena |
| Goddess of wisdom |
| Beckendorf |
| Hephaestus cabin member (reference) |
| Black Pegasus |
| Dark winged horse |
| Cadmus |
| Child of Zeus |
| Calypso |
| Sorceress |
| Cerberus |
| Three-headed dog |
| Charybdis |
| Sea monster |
| Chiron |
| Camp Half-Blood activities director |
| Circe |
| Sorceress. Aka: C.C. |
| Confederate Zombie Sailors |
| Crew |
| CSS Birmingham Captain |
| Undead Confederate officer |
| Demeter |
| Goddess of agriculture |
| Dionysus |
| Camp director. Aka: Mr. D |
| Eris |
| Goddess of discord |
| Europa |
| Child of Zeus |
| Fates |
| Controllers of destiny |
| Furies |
| Spirits of vengeance |
| Ganymede |
| Mythological figure (voice in taxi) |
| George |
| Snake in Hermes' staff |
| Hades |
| God of the Underworld |
| Harpies |
| Camp creatures |
| Hecate |
| Goddess of magic |
| Hellhound |
| Underworld monster |
| Hephaestus |
| God of fire and metalworking |
| Heracles |
| Hero (Greek name of Hercules) |
| Hercules |
| Hero (reference) |
| Hermes |
| Messenger god |
| Hippocampi |
| Sea creatures |
| Hydra |
| Multi-headed monster |
| Hylla |
| Circe's assistant |
| Iris |
| Goddess of the rainbow |
| Jason |
| Hero of the Golden Fleece |
| Kronos |
| Titan, main antagonist |
| Lord of the Flies |
| Book used for an English exam |
| Martha |
| Snake in Hermes' staff |
| Medea |
| Mythological sorceress (reference) |
| Medusa |
| Turns people to stone |
| Minotaur |
| Mythological monster |
| Nereids |
| Sea spirits |
| Odysseus |
| Mythological hero. Aka: Nobody |
| Oracle of Delphi |
| Gives prophecies |
| Oreius |
| Twin, Luke's assistant |
| Pan |
| God of the wild |
| Party Ponies |
| Chiron's relatives |
| Pegasus |
| Winged horse |
| Perseus |
| Hero who saved Andromeda |
| Polyphemus |
| Cyclops who captured Grover |
| Poseidon |
| Percy's father |
| Rainbow |
| Tyson's hippocampus |
| Scylla |
| Sea monster |
| Sirens |
| Enchant sailors |
| Tantalus |
| New camp activities director |
| Tempest |
| One of the Gray Sisters |
| Tyson |
| Percy's friend, a Cyclops |
| Wasp |
| One of the Gray Sisters |
| Zeus |
| God of the sky |
