The Argonauts and Mount Pelion
Aeson's half-brother, Pelias, seized the throne and threatened to kill the newborn Jason.
Jason learned that he was the rightful heir to the throne of Iolcus, currently held by the usurper Pelias.
Hera, who harbored a grudge against Pelias, saw in Jason a means to enact her revenge.
During the crossing, he lost one of his sandals, fulfilling a prophecy that Pelias had been warned about—that a man with one sandal would be his downfall.
When Jason arrived in Iolcus, he confronted Pelias.
Recognizing the man with one sandal, Pelias pretended to welcome him but, wary of the prophecy, devised a plan to rid himself of the threat.
He told Jason that he would surrender the throne if Jason could bring him the Golden Fleece, an impossible task that Pelias believed would lead to Jason's death.
Upon their return to Iolcus, Jason presented the Golden Fleece to Pelias.
However, instead of relinquishing the throne, Pelias reneged on his promise.
Medea then used her sorcery to trick Pelias' daughters into killing their father, believing they were making him young again.