In Greek mythology, Megareus of Onchestus was king of Onchestus in Boeotia. He was either son of Poseidon and Oenope, daughter of Epopeus[1], or of Onchestus (eponym of their kingdom), or of Apollo, or of Aegeus,[2] or of Hippomenes[3]. He came with his army to the assistance of Nisos, husband of his sister Abrota[4], against Minos. In one version, he died in the battle, and the city of Nisa (Nisos' domain) was renamed Megara in his honor[3][5]; in another, he married Iphinoe, daughter of Nisos, and succeeded to his father-in-law's power over Megara[6]. His children by Iphinoe were Evippus, Timalcus, and Evaechme; he also had a son Hippomenes by Merope[7]. With the aid of the god Apollo, Alcathous killed the Cithaeronian lion, for which Megareus gave him his daughter Euaechme as a wife. He subsequently made Alcathous his successor, because his own sons did not outlive him: Evippus was killed by the lion, and Timalcus was slain by Theseus, having joined the Dioscuri in the campaign against him.[8]