Who are the two villains in Jason and the Golden Fleece?

In the myth of Jason and the Golden Fleece, the two primary villains are King Pelias and the sorceress Medea. King Pelias, who usurps the throne of Iolcus, sends Jason on the dangerous quest to retrieve the Golden Fleece, hoping he will never return. Medea, initially an ally who helps Jason succeed, later becomes a tragic antagonist due to her desperate actions stemming from betrayal and heartbreak.