1. A son of Proetus, was king of Argos, and father of Anaxagoras and Iphianeira. (Paus. ii. 18. § 4; Diod. iv. 68.) He exchanged his dominion for that of Perseus, so that the latter received Tiryns instead of Argos. (Apollod. ii. 4. § 4; Paus. ii. 16. § 3.) He is said to have afterwards slain Perseus. (Hygin. Fab. 244.)
2. A son of Menelaus by an Aetolian slave, Pieris or Teridae. Menelaus brought about a marriage between Megapenthes and a daughter of Alector. (Hom. Od. iii. 188, iv. 11, xv. 100; Apollod. iii. 11. § 1.) 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. (Paus. iii. 19. § 2 ; comp. ii. 18. § 5, iii. 18. § 7.)
3. A third personage of this name occurs in Eustathius (ad Hom. p. 1480).