Percy Jackson
The narrator and hero of the book, Percy is a thirteen-year-old demigod who is the son of Poseidon.
Grover
One of Percy's two best friends, a satyr who used to guide demigods to Camp Half-Blood. While searching for Pan, he is captured by Polyphemus and taken to the Sea of Monsters.
Annabeth Chase
Percy's other best friend from camp, a daughter of Athena who he met last summer. Smart and a little cocky, Annabeth accompanies Percy on his quest to find Grover.
Tyson
Percy's friend from school, who is bullied because he is homeless and because people think he's ugly. As the novel continues, we learn that Tyson is in fact, a Cyclops, and Percy's half-brother.
Polyphemus
A Cyclops most recognizable from his role in the Greek epic, the Odyssey. In The Sea of Monsters, he has captured dozens of satyrs that were looking for Pan using the allure of the Golden Fleece.
Tantalus
The new activities director at Camp Half-Blood after Chiron is fired for allegedly poisoning Thalia's tree. A figure of Greek myth whose sin against the gods was so horrible that they sentenced him to constantly being tempted by food but never being able to eat it.
Luke Castellan
A son of Hermes who left Camp Half-Blood to work for Kronos, an evil Titan. He feels betrayed by the gods, particularly his father Hermes, and is set on destroying them.
Thalia Grace
A daughter of Zeus who died saving Luke, Annabeth, and Grover, Thalia was turned into a tree as she was dying, and this tree now protects Camp Half-Blood from monsters. At the end of the novel, the Golden Fleece brings her back to life.
Chiron
The original activities director of Camp Half-Blood and a centaur. The mythological mentor of heroes like Achilles and Hercules, Chiron advises Percy and his friends as they navigate the Sea of Monsters. As Kronos's son, he is initially under suspicion for poisoning Thalia's tree.
Clarisse
Daughter of the god of war, Ares, Clarisse is Percy's former bully and is favored by Tantalus over Percy and Annabeth. She is the one sent on the official quest to retrieve the Golden Fleece when Tantalus refuses to let Percy or Annabeth go.
Hermes
The Greek messenger god, as well as the god of thieves and of medicine. Hermes helps Percy go on his quest behind Tantalus's back, both because he wants to help Percy and because he wants Percy to try to reach out to Luke.
Mr. D
The director of Camp Half-Blood, who is really the Greek god Dionysus. He is at camp as a punishment from Zeus and doesn't really care for any of the campers.
Kronos
The main antagonist of the series, a Titan who wishes to return and destroy the gods, who are his children, once and for all. He is currently in a sarcophagus trying to rebuild his body so that he can reform.
