Iolcus (eye-AWL-kus). Thessalian city from which Jason and the Argonauts set out after the Golden Fleece. Jason's father should have been king of Iolcus, but his brother Pelias had usurped the throne. So when Jason, who had been raised in the wilderness by Chiron the centaur, arrived in Iolcus and asserted his claim to the kingdom, Pelias sent him after the Golden Fleece to be rid of him.