Medea used magic to make it possible for Jason to accomplish the tasks set for him. The king however would not keep his promises, so Jason stole the golden fleece and left. He took Medea with him and married her.
It was because of Medea that Jason did get the throne of Iolcus. Medea delayed the raging AeŽtes from pursuing them by slitting her brother's throat and dismembering him. She threw the pieces overboard one by one, allowing them to escape as AeŽtes picked up each piece to bury it, making him lose track of the Argonauts.
When they reached Iolcus, Medea pursuaded Pelias's daughters to kill their father and boil him in a couldron to 'find new youth'. Once this had been done, the way was clear for Jason to take the throne.
Jason and Medea lived happily in Iolcus and then for several years in Corinth, until Jason realised that his children were not acceptable heirs to the throne because their mother was a barbarian. Jason divorced Medea and married CreŁsa, daughter of King Creon of Corinth. Medea was true to her evil past. She sent a robe as a wedding present to Jason's new wife; the robe was impregnated with a deadly poison, which killed CreŁsa as soon as she put it on. When Creon rushed to help his daughter he too was poisoned. In her rage, Medea also killed her two children by Jason before escaping in an airborne chariot. As Jason in total despair sat brooding on his misfortune under the hulk of the Argo, with which he had won all his glory, a beam fell from the ship and killed him.