In Greek mythology, Aeson or Aison (Ancient Greek: Αἴσων) was the son of Cretheus and Tyro, who also had his brothers Pheres and Amythaon. Aeson was the father of Jason and Promachus with Polymede, the daughter of Autolycus. Other sources say the mother of his children was Alcimede or Amphinome. Aeson's mother Tyro had two other sons, Neleus and Pelias, with the god of the sea Poseidon.
Pelias was power-hungry and he wished to gain dominion over all of Thessaly. To this end, he banished Neleus and Pheres and locked Aeson in the dungeons in Iolcus. Aeson sent Jason to Chiron to be educated while Pelias, afraid that he would be overthrown, was warned by an oracle to beware a man wearing one sandal.
Many years later, Pelias was holding the Olympics in honor of Poseidon when Jason, rushing to Iolcus, lost one of his sandals in a river while helping Hera (Juno), in the form of an old woman cross. When Jason entered Iolcus, he was announced as a man wearing one sandal. Paranoid, Pelias asked him what he (Jason) would do if confronted with the man who would be his downfall. Jason responded that he would send that man after the Golden Fleece. Pelias took that advice and sent Jason to retrieve the Golden Fleece.
During Jason's absence, Pelias intended to kill Aeson. However, Aeson committed suicide by drinking bull's blood. His wife killed herself as well, and Pelias murdered their infant son Promachus.
Alternatively, he survived until Jason and his new wife, Medea, came back to Iolcus. She slit Aeson's throat, then put his corpse in a pot and Aeson came to life as a young man. She then told Pelias' daughters she would do the same for their father. They slit his throat and Medea refused to raise him, so Pelias stayed dead.