Luke Castellan is a son of the Greek god Hermes and a major antagonist of Rick Riordan's Percy Jackson and the Olympians series. He holds a grudge against the gods, and is trying to awaken the Titan Kronos (also known as Cronus) to destroy the Olympian gods. Luke also serves as the protagonist and narrator of The Demigod Diaries story The Diary of Luke Castellan (which takes place five years before the events of The Lightning Thief).