Megapenthes was a son of Proetus and the cousin of Perseus.
Megapenthes was a son of Proetus, a king of Argos and Tiryns. He exchanged kingdoms (Argos for Tiryns) with his cousin Perseus, whom he killed much later. He was the father of Argeus and possibly Anaxagoras (or else Anaxagoras was his grandson through Argeus). He also had a daughter Iphianeira, who married Melampus.