Surtur is the Lord and Ruler of Musphelheim, the fire realm of Asgard.  He is a humanoid who stands as tall as the Frost Giants of Jotunheim, but he is a creature of fire and flame.For centuries Surtur has been contained in Muspelheim, but he was released when the wards between the worlds were weakened by Baron Zemo.  

When the Enchantress was teleported to Muspelheim, Surtur wasted no time in possessing her and making her his minion, enhancing her powers and supressing her own will with his own.

Surtur has reclaimed the shards of his sword, and re-forged it.  It is said that the power of his sword will consume all of the worlds in fire.