In
Greek mythology,
Megareus of Onchestus was king of
Onchestus in
Boeotia. He was either son of
Poseidon and Oenope, daughter of
Epopeus, or of Onchestus (
eponym of their kingdom), or of
Apollo, or of
Aegeus, or of Hippomenes. He came with his army to the assistance of
Nisos, husband of his sister
Abrota, against
Minos. In one version, he died in the battle, and the city of Nisa (Nisos' domain) was renamed Megara in his honor; in another, he married
Iphinoe, daughter of Nisos, and succeeded to his father-in-law's power over Megara. His children by Iphinoe were Evippus, Timalcus, and Evaechme; he also had a son
Hippomenes by Merope. With the aid of the god
Apollo,
Alcathous killed the
Cithaeronian lion, for which Megareus gave him his daughter
Euaechme as 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.