1. A son of Proetus, was king of Argos, and father of Anaxagoras and Iphianeira. He exchanged his dominion for that of Perseus, so that the latter received Tiryns instead of Argos. (Apollodorus. ii.) He is said to have afterwards slain Perseus.
2. A son of Menelaus by an Aetolian slave, Pieris or Teridae. Menelaus brought about a marriage between Megapenthes and a daughter of Alector. (Apollodorus. ii.) According to a tradition current in Rhodes, Megapenthes, after the death of his father, expelled Helen from Argos, and she fled to Polyxo at Rhodes.
A third personage of this name occurs in Eustathius (ad Horn.