Gyges

Gyges (Γύγη in Ancient Greek) was one of the three Hekatonkhires (Hundred Handed Ones), who helped in the war with the Titans, after Zeus freed them from Tartarus, by throwing hundreds of rocks at the Titans. He faded away, along with his brother Cottus, after humans forgot his story, leaving only Briares.

The Battle of the Labyrinth
Gyges is mentioned by Briares (another Hekatonkhire) when talking to Percy, Annabeth, Grover and Tyson.