Jason,"ΙΑΣΩΝ" in Greek, is a hero of Greek mythology. His father was Aeson, the rightful king of Iolcus. His real name was Diomedes and he changed it to Jason (which means "healer" or "doctor") after having studied therapeutic herbs under the guidance of the centaur Cheiron.
The Early Years
Pelias (Aeson's half-brother) was power-hungry and he wished to gain dominion over all of Thessaly. Pelias was the product of a union between their shared mother (high born Tyro, daughter of Salmoneus) and the sea god Poseidon. In a bitter feud, he overthrew Aeson (the rightful king), killing him and hopefully his descendants, who might take revenge on him. Polymede (wife of Aeson) already had an infant son by Aeson, Jason who she sent to the centaur (half man, half horse) Cheiron for education, for fear that Pelias would kill him - she claimed that he had been killed (circumstances unclear). Pelias, paranoid 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 arrived in Iolcus and lost one of his sandals in the river Anavros, while helping an old woman (Goddess Hera in disguise) cross. She blessed him for she knew, as goddesses do, what Pelias had up his sleeve. 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 as he thought it an impossible mission for this young lad that stood before him (Jason was supposed to have been about 18-20? at the time).
Pelias sends forth Jason, in an 1879 illustration from Stories from the Greek Tragedians by Alfred Church
Jason and Orpheus
The quest for the Golden Fleece
Jason assembled a great group of heroes and a huge ship called the Argo. Together, the heroes were known as the Argonauts. They included the Boreads, Heracles, Telamon, Orpheus, Castor and Polydeuces, Atalanta and Euphemus.
The Isle of Lemnos
The isle of Lemnos is situated off the Western coast of Asia Minor (modern day Turkey). The island was inhabited by a race of women, who had killed their husbands. The women had apparently neglected their worship of Aphrodite (goddess of love), and so as a punishment the goddess made the women so smelly that their husbands couldn't bear to be near them, so they took concubines from the Thracian mainland opposite. The women, naturally angry, killed every male inhabitant (the king, Thoas, was saved by Hypsipyle, his daughter, who put him out to sea in a chest and was picked up by someone.). They lived for a while without men, with Hypsipyle as their queen.
The Argonauts stopped off here, and the women welcomed them with open arms. Jason fathered twins with the queen, and many other Argonauts fathered children with the other women, therefore reintroducing a male population to the island (the offspring were male). They left for the Golden Fleece after spending a considerable amount of time on the island. Heracles pressured them to go as he was disgusted by the antics of the Argonauts (he, himself, didn't take part, which is truly unusual, considering the numerous affairs he had with other women) - he is the moral voice throughout - he reminds the crew of their mission.
The arrival In Colchis
Jason, a highly personal, dreamlike reinterpretation by the Symbolist Gustave Moreau, 1865
Jason arrived in Colchis to claim the fleece as his own. King Aeetes of Colchis promised to give it to him only if he could perform certain tasks. First, Jason had to plow a field with fire-breathing oxen that he had to yoke himself. Medea provided an ointment that protected him from the oxen's flames. Then, Jason sowed the teeth of a dragon into a field. The teeth sprouted into an army of warriors. Medea had previously warned Jason of this and told him how to defeat this foe. Before they attacked him, he threw a rock into the crowd. Unable to decipher where the rock had come from, the soldiers attacked each other and defeated each other. Finally, Jason had to fight and kill the sleepless dragon that guarded the fleece, but again Medea used her magic to put the dragon to sleep. Jason then took the fleece and sailed away with Medea, who had fallen in love with him and helped him win the fleece. Medea distracted her father as they fled by killing her brother, Apsyrtus. In the flight, Atalanta was seriously wounded but healed by Medea.
On the way back to Thessaly, Medea prophesised to Euphemus, the Argo's helmsman, that one day he would rule Libya. This came true through Battus, a descendant of Euphemus.
When the Argonauts stopped on Aeaea, Circe purified them for the death of Apsyrtus.
Chiron had told Jason that without the aid of Orpheus, the Argonauts would never be able to pass the Sirens. The Sirens lived on three small, rocky islands called Sirenum scopuli and sang beautiful songs that enticed sailors to come to them. They then ate the sailors. When Orpheus heard their voices, he withdrew his lyre and played his music more beautifully than they, drowning out their music.
The Argo then came to the island of Crete, guarded by the bronze man, Talos. Talos had one vein which went from his neck to his ankle, bound shut by only one bronze nail. Medea cast a spell on Talos to calm him; she removed the bronze nail and Talos bled to death. The Argo landed.
While Jason searched for the Golden Fleece, Hera, who was still angry at Pelias, conspired to make him fall in love with Medea, whom she hoped would kill Pelias. When Jason and Medea returned, Pelias still refused to give up his throne. Medea conspired to have Pelias' own daughters kill him. She told them she could turn an old ram into a young ram by cutting up the old ram and boiling it. During the demonstration, a live, young ram jumped out of the pot. Excited, the girls cut their father into pieces and threw them into a pot. Pelias did not survive.
Jason and Medea then had to flee to Corinth.
Jason was later driven into exile by Acastus, and came to Corinth. There he abandoned Medea, and she killed their children and fled. Alternatively, he married Creusa in Corinth. Medea got even by giving Creusa a cursed dress that stuck to her body and burned her to death as soon as she put it on. She also killed Creusa's father, Creon, and her own sons with Jason. Later Jason and Peleus would attack and defeat Acastus, reclaiming Iolcus for his house. Jason's son, Thessalus, then became king.
Later Jason was killed when the timbers of the Argo rotted and the mast fell on him.
Though some of the episodes of Jason's story draw on ancient material, the definitive telling, on which this account relies, is that of Apollonius of Rhodes in his epic poem Argonautica, written in Alexandria in the late 3rd century BC.
The mythical geography of the voyage of the Argonauts has been speculatively explicated by the historian of science and the cartography of Antiquity, Livio Catullo Stecchini, in a suggestive essay "The Voyage of the Argo" (http://www.metrum.org/mapping/argo.htm) that draws upon fragments of the mythic sources Apollonius employed in constructing his poem.
In the Divine Comedy Dante sees Jason in the eighth circle of Hell among the seducers.
The Argonautica by Apollonius Rhodius
R. J. Clare, The path of the Argo : language, imagery and narrative in the Argonautica of Apollonius Rhodius (Cambridge Classical Studies) Cambridge University Press 2002, ISBN 0521810361
Medea and Jason , Edmund Dulac (1882-1953)