| The |
Albino Lion | Zoo animal freed by Percy and Grover |
| The |
Antelope | Zoo animal freed by Percy and Grover |
| Nancy |
Bobofit | Kleptomaniac bully and Percy's classmate |
| Napoleon |
Bonaparte | Mortal compared to Hades's gaze |
| The |
Bus Driver | Drives Percy and Grover toward Manhattan |
| Luke |
Castellan | Son of Hermes; counselor of Cabin Eleven |
| Annabeth |
Chase | Percy's friend; daughter of Athena. Aka: Wise Girl |
| The |
Coast Guard Officers | Rescue Percy, Annabeth, and Grover |
| The |
Council of Cloven Elders |
Judges Grover's keeper performance |
| The |
Cyclopes | The one-eyed being from Percy's childhood; forgers of Zeus's master bolt |
| The |
Dryads | Wood nymphs |
| The |
Gang Leader | Mortal teenage delinquent |
| The |
Gang Members | Mortal teenage delinquents |
| Thalia |
Grace | Daughter of Zeus; transformed into a pine tree |
| The |
Headmaster | Headmaster of Yancy Academy |
| Adolph |
Hitler | Mortal compared to Hades's gaze |
| Percy |
Jackson | Protagonist; demigod son of Poseidon. Aka: Seaweed Brain, Perseus |
| Sally |
Jackson | Percy's mother |
| Thomas |
Jefferson | Example of a judge of the dead |
| Mrs. |
Kerr | Teacher who replaces Mrs. Dodds in everyone's memory |
| Clarisse |
La Rue | Daughter of Ares; counselor of Ares's cabin |
| The |
Lotus Bellhop | Attempts to trap the trio in the casino |
| The |
Lotus Casino Doorman | Lures the trio into the casino |
| The |
Math Teacher | Taught Percy before Mrs. Dodds |
| King |
Minos | One of the judges of the dead |
| The |
Minotaur | Mythological monster who hunts Percy |
| The |
Mortal Family | Family Percy protects from the Chimera |
| The |
Mortal Police | Publish Percy's photo and label him a fugitive |
| The |
Naiads | Water nymphs who flirt with Percy |
| The |
Newspaper Reporters | Publish Percy's photo and label him a fugitive |
| Mr. |
Nicoll | Percy's English teacher |
| The |
Nine Muses | Goddesses of the arts |
| The |
Older Demigods | Camp Half-Blood campers |
| The |
Olympian Gods | Gods assigned as patrons to cabins |
| The |
Oracle of Delphi | Delivers prophecies to demigods |
| The |
Other Satyrs | Camp Half-Blood satyrs |
| The |
Other Two Furies | Sisters of Mrs. Dodds |
| The |
Other Two Gorgons | Medusa's sisters |
| The |
Owner | Gladiola's owner who rewards the trio |
| The |
Park Ranger | Witnesses the Chimera |
| The |
Pit Scorpion | Used by Luke to attack Percy |
| The |
Plump Blond Boys | Children of Dionysus |
| The |
Python | Ancient serpent slain by Apollo |
| The |
River Catfish | Helps Percy hide from the Chimera |
| The |
School Counselor | Claims Percy's behavior is due to ADHD |
| The |
Security Ghouls | Underworld guards |
| William |
Shakespeare | Example of a judge of the dead |
| The |
Skeleton Warriors | Guard Hades's palace |
| Eileen |
Smythe | Mortal journalist |
| The |
Surfer | Believes Percy speaking to sharks is a hallucination |
| The |
Taxi Driver | Drives Percy from the bus terminal to his apartment |
| The |
Televangelist Preacher | Seized by Underworld guards |
| The |
Terrorist Leaders | Mortals compared to Hades's gaze |
| Gabriel |
Ugliano | Percy's abusive stepfather. Aka: Smelly Gabe |
| Grover |
Underwood | Percy's best friend; a satyr |
| The |
Waitress | Enchanted by Ares |
| Barbara |
Walters | Mortal television journalist |
| George |
Washington | Demigod son of Athena |
| The |
Wild Boar | Monster summoned by Ares |
| The |
Wood Nymph | Dionysus's lover |
| The |
Zebra | Zoo animal freed by Percy and Grover |
| Alecto |
| Percy's pre-algebra teacher; a Fury. Aka: Mrs. Dodds |
| Aphrodite |
| Goddess of love and beauty; Poseidon's aunt. Aka: Venus |
| Apollo |
| God of music and prophecy; son of Zeus. Aka: Phoebus |
| Arachne |
| Source of Annabeth's fear of spiders |
| Ares |
| God of war; manipulates Percy |
| Argus |
| Camp Half-Blood's guard; a many-eyed giant |
| Artemis |
| Goddess of the hunt and maidenhood |
| Athena |
| Goddess of wisdom and battle; Annabeth's mother |
| Cerberus |
| Three-headed guard dog of the Underworld |
| Charon |
| Ferryman who helps the trio cross the River Styx |
| Chimera |
| Monster Percy mistakes for a chihuahua |
| Chiron |
| Percy's Latin teacher; Camp Half-Blood's director; a centaur. Aka: Mr. Brunner |
| Darrin |
| Helps Percy realize the casino distorts time |
| Demeter |
| Goddess of agriculture |
| Dionysus |
| Director of Camp Half-Blood; god of wine. Aka: Mr. D |
| Echidna |
| Mother of the Chimera |
| Eddie |
| One of Gabe's poker buddies |
| Eddie |
| Zoo truck driver |
| Fates |
| Three goddesses who control the thread of life |
| Ferdinand |
| Grover's uncle; a satyr. Aka: Uncle Ferdinand |
| Furies |
| Mythological spirits of vengeance. Aka: Kindly Ones |
| Gladiola |
| Pink poodle who communicates with Grover |
| Hades |
| God of the Underworld; holds Percy's mother captive. Aka: Lord of the Dead |
| Hellhounds |
| Monsters from the Underworld |
| Hephaestus |
| God of fire and metalworking; ally of Ares |
| Hera |
| Goddess of marriage; wife of Zeus. Aka: Queen of the Gods |
| Hercules |
| Legendary Greek hero |
| Hermes |
| Messenger god; patron of Cabin Eleven |
| Hestia |
| Goddess of the hearth; prevents war |
| Houdini |
| Mortal who survived the Underworld |
| Iris |
| Goddess of rainbows and messenger of the gods |
| Jason |
| Hero of the Argonauts |
| Kronos |
| Father of the Olympian gods; voice in Percy's nightmares. Aka: Crooked One, The Thing in the Pit |
| Maurice |
| Zoo truck driver |
| Medusa |
| Gorgon who aids Percy. Aka: Aunty Em |
| Nemesis |
| Goddess of revenge |
| Nereid |
| Sea nymph who helps Percy for Poseidon |
| Orpheus |
| Mortal who survived the Underworld |
| Ouranos |
| Primordial god; father of Kronos |
| Pan |
| God of the wild and nature |
| Pasiphae |
| Mythological mother of the Minotaur |
| Persephone |
| Queen of the Underworld |
| Polydeuces |
| Mistaken by Percy for Polydictes |
| Polydictes |
| Mistaken by Percy for Polydeuces |
| Poseidon |
| God of the sea; Percy's father. Aka: White Horse |
| Procrustes |
| Son of Poseidon. Aka: Crusty |
| Prometheus |
| Titan mentioned by Chiron |
| Rhea |
| Mother of the Olympian gods; Zeus's mother |
| Sisyphus |
| Condemned to push a boulder eternally |
| Sugar |
| Mortal woman accompanying Gabe |
| Theseus |
| Original slayer of the Minotaur |
| Zephyr |
| Wind god who delivers Annabeth |
| Zeus |
| God of the sky; accuses Poseidon of stealing his master bolt. Aka: Golden Eagle, Jupiter |
