Surtur was native to the extra-dimensional plane of Muspelheim and was the mortal enemy of the Asgardian ruler Odin and his son Thor. Surtur and the demonic Frost Giant Ymir were older, and therefore more powerful, immortals than Odin and Thor, who were always hard pressed to defeat them. The two demons were once summoned to Earth together when the Spell of Fire and Ice was cast by the Sons of Satannish.