Jason is the Greek legendary hero best known for his leadership of the Argonauts in the quest for the Golden Fleece and for his wife Medea (of Colchis).
Jason As the 1-Sandaled Man
Now Jason loved husbandry and therefore abode in the country, but he hastened to the sacrifice, and in crossing the river Anaurus he lost a sandal in the stream and landed with only one. - Apollodorus
Early in his career, Jason carried an old woman across the Anauros or Enipeus River. She was no ordinary mortal, but Hera, in disguise. In the crossing, Jason lost a sandal, and so appeared as the man in one sandal (monosandalos) foretold to kill King Pelias. Another explanation for Jason's loss of a sandal is that he might have been plowing when he stepped into the river without having fastened his sandal tight first.
1.9.16 Aeson, son of Cretheus, had a son Jason by Polymede, daughter of Autolycus. - Apollodorus
Jason's father was Aison (Aeson). His mother was Polymede, a possible daughter of Autolycus. Aison was the oldest son of winds ruler Aeolus' son Cretheus, founder of Iolchus, which should have made Aison king of Iolchus, instead of Pelias, Cretheus' stepson.
Fearing for their son after Pelias usurped the throne, Jason's parents pretended their baby had died at birth. They sent him to the wise centaur Chiron to be raised. Chiron may have named the boy Jason (Iason).
Jason's main homes were Thessaly (Iolchus and Mt. Pelion) and Corinth (Greece).
The Task of Fetching the Golden Fleece
The explanations for why Jason was sent revolve around the issue of Pelias' occupying a throne for which Jason thought his side of the family had a better claim.
The simplest explanation is that the fleece was the price of becoming king. Pelias could keep the herds and land, but the throne would go to the direct line of Cretheus after Jason brought back the golden fleece.
The more popular story is that Pelias, having told the one-sandaled stranger that his death at the hand of a fellow-citizen had been foretold, asked Jason what he would do. Jason said to send him for the fleece. So Pelias ordered Jason to do so.
Jason Marries Medea
On the return voyage of the Argonauts, they stopped at the island of the Phaeacians, ruled by King Alcinoos and his wife Arete (featured in "The Odyssey"). Their pursuers from Colchis arrived at about the same time and demanded the return of Medea. Alcinoos agreed to the Colchians' demand, but only if Medea weren't already married. Arete secretly arranged the marriage between Jason and Medea, with Hera's blessings.
Jason Returns Home and Leaves Again
There are various tales of what happened when Jason returned to Iolchus, but the one that is best known is that Pelias was still alive, so Medea tricked his daughters into killing him. She pretended that she would restore Pelias not just to life, but to youthful vigor.
After killing Pelias, Medea and Jason took off, again, to Corinth, a place where Medea had a claim to the throne, as the granddaughter of the sun god Helios.
Jason Deserts Medea
Hera also favored Medea, as well as Jason, and offered their children immortality.
2.3.11 Through her Jason was king in Corinth, and Medea, as her children were born, carried each to the sanctuary of Hera and concealed them, doing so in the belief that so they would be immortal. At last she learned that her hopes were vain, and at the same time she was detected by Jason. When she begged for pardon he refused it, and sailed away to Iolcus. For these reasons Medea too departed, and handed over the kingdom to Sisyphus. - Pausanias
In the Pausanias version, Medea engages in the sort of helpful, but misunderstood behavior that scared Achilles' father and Metaneira of Eleusis, who witnessed Demeter's attempt to immortalize her baby. Jason could only believe the worst of his wife when he saw her engaging in such a dangerous activity, so he deserted her.
Of course, the version of Jason's desertion of Medea told by Euripides is much more sinister. Jason decides to repudiate Medea and marry the Corinthian king Creon's daughter, Glauce. Medea doesn't accept this change in status gracefully but arranges the death of the king's daughter by poison gown, and then kills the 2 children she has borne Jason.
Death of Jason
The death of Jason isn't as popular a topic of classical literature as his adventures. Jason may have killed himself or fallen victim to a decaying plank from his ship, the Argo.