It is in the story of Jason and his group of Argonauts . They set out on a quest ordered by King Pelias to get the fleece so that Jason can rightfully claim the throne of Iolcus in Thessaly . It figures in the tale of Jason and his band of Argonauts , who set out on a quest by order of King Pelias for the fleece in order to place Jason rightfully on the throne of Iolcus in Thessaly .