Odin, ruler of Asgard, and Gaea created a child of both Asgard and Midgard (Earth). Thor was taken to Asgard to be raised by Odin's wife Frigga. On Thor's eighth birthday, Odin had the magical hammer Mjolnir created, to be presented to Thor once he proved to be a worthy warrior. Eight years later, he succeded and Odin presented Mjolnir to Thor, declaring him the greatest warrior in Asgard.