The Greek Olympian gods are a major part of the Percy Jackson universe and story, as they're essentially the main impetus for everything that happens. Every demigod at Camp Halfblood is the child of one of these gods, and they often end up having to go on quests to fix the messes that the gods started themselves. These god characters are all based on real-life Greek mythology, though some liberties have been taken regarding how their personalities and stories are depicted.