Percy Jackson: The son of Poseidon; a 13-year-old demigod who travels to the island of Polyphemus in the Bermuda Triangle to find Grover and recover the Golden Fleece. He is accompanied by Annabeth and Tyson, his half-brother, on the quest. He is successful in the end; and gives Clarisse the Fleece while he is attacked by Luke on his way to the Camp. However, he and his friends are rescued by Chiron and the Party Ponies.
Annabeth Chase: The daughter of Athena. A demigod who is 13 years old and a friend of Percy. She accompanies him to the island and helps him in his quest by rescuing Percy from Circe's island. Annabeth is injured by Polyphemus and recovers with the help of the Golden Fleece. She accompanies Percy to Camp after Chiron succeeds in rescuing them from the hands of Luke and the Titan army.
Grover Underwood: The guard for Percy given by the gods, a satyr who has been captured by Polyphemus during his search for the wild god Pan. Due to his poor eyesight, Polyphemus mistakes Grover for a female Cyclops. He is rescued by his friends Percy and Annabeth.
Clarisse La Rue: Daughter of Ares who was given the quest of retrieving the Golden Fleece. With the help of Percy and his friends, she is successful in her quest. Percy gives her the Fleece that she takes to Camp Half Blood. Polyphemus wishes to wed her after it is revealed to him that Grover is a male satyr.
Luke Castellan: The main antagonist, now 20; he works for Kronos. He captures Percy and the rest before being thwarted by Chiron and his brethren, the Party Ponies.
Tyson the Cyclops: Percy's half brother; he is initially portrayed as a homeless child before Annabeth helps Percy realize that he is a Cyclops. He accompanies Percy and Annabeth in their quest and befriends a hippocampus whom he names Rainbow.He is very big and has one brown eye. When Clarisse's ship explodes, he is presumed dead until it is learned that he was actually saved.