Surtur

Surtur is a fire demon from the extra-dimensional planes of Muspelheim.

The Forging
Surtur possessed Enchantress and attacked with his army the home world of Beta Ray Bill, Korbin. At the burning planet, he forged the Twilight Sword. After the Enchantress was defeated by Thor and Bill, he cleared the forging of his sword.

Role in the Series
In the Spongebob series, Surtur is revealed to be one of the original Darkspawn Lords, the Lord of Hellfire and Brimstone, who fought during the First Cartoonian War against the High Council's 7 Guardians of Light. During the Clash of Blades, Surtur's keyblade, the Twilight Sword, clased with that of a light keyblade, leading to the forging of the X-blade, and the start of the Keyblade War to obtain its great power. Eventually, it was the leader of the 7 Guardians who became the wielder of the x-blade, and used its power to defeat Chernabog and his Darkspawn Minions. Surtur was selectively banished to a private sector of Hell known as Muspelheim so that his great power would not destroy Hell in the process. His chair in the New Seekers of Darkness has been succeeded by the corrupted Isa, who, like Surtur, is the Berserker of the bunch.