Jason is the son of Aeson. As a child he is given to the centaur, Chiron, to be raised, educated, and protected from his greedy half-uncle, Pelias, king of Iolocus. In an effort to get rid of Jason, Pelias sends him in quest of the Golden Fleece, but, with Medea's help, Jason succeeds in obtaining it.

Jason can be considered the play's villain, though his evil stems more from weakness than strength. A former adventurer, he abandons his wife, Medea, in order to marry Glauce, the beautiful young daughter of Creon, King of Corinth.

In the legend of Jason and the Golden Fleece, Medea, the princess of Colchis, helps Jason steal the Golden Fleece from her father. Euripides draws inspiration from this legend. However, Medea depicts Jason not as a hero but as a faithless husband who abandons his wife.

Jason is a middle-aged man, with much glory, indeed, and some illusions; but a man entirely set upon building up a great career, to whom love and all its works, though at times he has found them convenient, are for the most part only irrational and disturbing elements in a world which he can otherwise mould to his will.

Jason is heir to the throne of the Greek kingdom of Iolcus. After his uncle Pelias usurps his father’s place, Jason spends his childhood hidden on Mt. Pelion, raised by the centaur Cheiron (the tutor of Achilles). When Jason comes of age, Pelias promises to return the throne to him—if he can complete a number of overwhelming tasks.