In Greek mythology, Megapenthes (Greek: Μεγαπένθης Megapénthēs) is a name that refers to:
A son of Proetus. 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.
A son of Menelaus, who ruled after his father's death and sent Helen into exile. In some legends, Helen was his mother; in most, however, he was Menelaus's son by a concubine, Pieris or Tereis, and was born during the Trojan War. His name means "great sorrow" and he is named that because he was born from an affair that Menelaus had while grieving at the loss of Helen. He marries the daughter of Alector in the beginning of Book IV of The Odyssey, whose name was Iphiloche or Echemela). together with Menelaus and Helen. Megapenthes and his brother or half-brother Nicostratus were depicted on the throne in Amyclae riding one and the same horse.
