Thessalus in Wikipedia

In Greek mythology, the name Thessalus is attributed to three individuals. * Thessalus was the son of Jason and Medea and the twin of Alcimenes. After the adventures of the Argonauts and the death of Acastus, Thessalus became king of Iolcus. He gave his name to the land of Thessaly, in which Iolcus lies. * Thessalus was also the name of a son of Heracles. * Thessalus was the name of the son of Haemon for whom Thessaly was named.