Lord of the Fire Giants
Surtr is the god of fire giants and war. His domain is war.
As a member of the giants' pantheon, Surtr answered to Annam, the Allfather. At the close of the Third Age, Tiamat (at the urging of Memnor) convinced the other deities turned against Annam's wife, who was a primordial. Feeling caught between their leader and their fellow deities, Surtr - along with Aegir, Stronmaus, and Thrym - chose to stand aside. When Annam's wife was killed, and Annam himself banished, the giants felt betrayed by their inaction and turned against their gods. Enraged, Surtr sequestered himself in his fortress in Ysgard, his fury simmering for thousands of years. In addition to the handful of fire giants who worshiped him, Surtr also found followers in a number of other evil fire creatures.
During the Deity War, Stronmaus convinced Surtr and Thrym to join him in exacting vengeance on Tiamat for her part in Annam's downfall. Together, the three gods and their servants traveled to Tytherion and assaulted Tiamat's citadel. The battle raged for days, and while countless of Tiamat's draconic and angelic servants were killed, the Dragon Queen herself proved too powerful. Surtr and Thrym were forced to flee, while Tiamat herself devoured Stronmaus.