In Greek mythology, Euphemus was the name of several distinct characters:Euphemus, son of Poseidon and an Argonaut. Euphemus, a descendant of the river god Axius and the father of the hero Eurybarus who defeated the female monster Sybaris. Euphemus, son of Troezenus and a leader of the Thracian Cicones. He was an ally of the Trojans. According to late writers, he was killed either by Achilles or by one of the following four: Diomedes, Idomeneus and the two Ajaxes who at one point united to attack the opponents. Euphemus, surname of Zeus on Lesbos.