In Greek mythology, Aeson was a king of Iolcus in Thessaly and father of the Argonaut Jason. Son of Cretheus and Tyro, he was displaced by his half-brother Pelias. Traditions diverge on his end: some have him die by poison before Jason's return; Ovid and others tell that Medea rejuvenated him as an old man.
Adapted from Wikipedia, "Aeson" · CC BY-SA 4.0
I.Family and the throne of Iolcus
Aeson was son of Cretheus, founder of Iolcus, and Tyro; his full brothers were Amythaon and Pheres. Through Tyro's liaison with Poseidon he was half-brother to Pelias and Neleus. Ancient authors disagree on Jason's mother—Alcimede, Polymede (daughter of Autolycus), Polymele, and others are named—and some add a younger son Promachus.
Pelias seized power in Thessaly, banished other kin, and kept Aeson from effective rule. Aeson sent the boy Jason to Chiron for fostering while an oracle warned Pelias to beware a one-sandaled man.
II.Jason's quest and Aeson's fate
When Jason returned wearing one sandal, Pelias sent him after the Golden Fleece. During the voyage one tradition has Pelias plot Aeson's death; Aeson then drinks bull's blood and dies, his wife following him, while Pelias kills infant Promachus.
In the alternative cycle preserved by Ovid, Aeson still lives when Jason and Medea return. Medea drains the old king's blood and restores him to youth in a cauldron—then tricks Pelias' daughters into attempting the same rite, which kills their father instead.