A character from the Ulster cycle of Irish mythology, he is the former king of Ulster who was tricked out of his kingship, and then later became the ally and lover of Medb. He helped raise his nephew Cu chulainn, and is known to be a huge womanizer. He wields the spiral sword Caladbolg.
He has a younger version of himself, known as Fergus mac Roich (young), who behaves nothing like his adult self.