He is portrayed by Robert Maillet.
Polyphemus is a Cyclops living on an island in the Sea of Monsters. He guards the Golden Fleece and uses it to lure satyrs and eat them. He is famous among the Cyclops because he captured Odysseus in his lair by blocking the entrance with a boulder.
In the past, Polyphemus reared a herd of sheep and he managed to lure satyrs every day with the Golden Fleece. Over the years, satyrs came less often and he was so hungry that he had to eat his own sheeps. Because of his hunger, his eyesight got worse and worse.
The goddess Circe built an amusement park for half-bloods named Circeland on top of his island. However, Polyphemus devoured many half-bloods during the opening day, which resulted in the abandonment of the park.
Luke Castellan sends some of his half-bloods henchmen and the satyr Grover Underwood to Polyphemus's island to get the Golden Fleece, that he wants use to resurrect Kronos. After their arrival into his lair, Polyphemus devours all of them, except Grover who disguises himself as a Cyclops chambermaid.
Two days later, the demigods Percy Jackson, Annabeth Chase, Clarisse La Rue and the Cyclops Tyson enters the lair while Polyphemus is yelling at Grover. Percy and Clarisse sneak behind him and try to seize the Golden Fleece on his shoulder, but Polyphemus smells them and attacks them. Tyson comes into his sight and tries to talk to him Cyclops to Cyclops, only to be insulted by Polyphemus. Percy takes advantage of the distraction to leap over Polyphemus and succeeds to snatch the Golden Fleece from him. After punching Tyson, Polyphemus goes after Percy and manages to catch him, but he throws the fleece to Annabeth, who then throws it to Clarisse, who throws it back to Percy. Grover distracts Polyphemus by removing his disguise and revealing him that he is a male satyr, much to his surprise. The five teenagers then flee to the exit pursued by Polyphemus and Grover unhooks a chandelier which falls on his path. Once they are all out of the lair, Tyson blocks the entrance with the boulder, imprisoning Polyphemus.