Megapenthes is the son of King Proetus. After his uncle Acrisius, former co-ruler of Argos with Proteus, gave Mycenae to his brother, he was accidentally killed by his grandson Perseus. Perseus, feeling guilty about becoming king, exchanged Argos for Meganpenthes' kingdom of Mycenae. Megapenthes then ruled Mycenae until he was succeeded by his son Argeos.