Pelias (pē´lēăs), in Greek mythology, usurper of the throne of Iolcus. He was the son of Tyro and Poseidon and the twin brother of Neleus. After his birth his mother married Cretheus, king of Iolcus, and gave birth to Aeson. After Cretheus' death Pelias seized power, killed (or imprisoned) Aeson, and exiled Neleus. Later Medea, hoping to restore Jason as rightful successor to the throne, tricked the daughters of Pelias into murdering him.