Surtr (ᛋᚢᚱᛏᚱ) is king of the fire jötunn in Norse mythology. He is a major figure in the events of Ragnarök where he is destined to kill Freyr.
There are very few descriptors as to Surtr's appearance. Most descriptors available describe the sword he carries with him. It is described as shining brighter than the sun. A burning blade capable of razing the world with a fiery inferno.
Surtr is quite possibly one of the most ancient and powerful beings in Norse myth as he hails from Muspelheim a realm of fire existing before the appearance of Niflheim.
In the events of Ragnarök he will ride from the south with his sons burning everything in their path. They will ride over the Bifröst which will in turn break it. At this point Loki, Fenrir, Jörmungandr, the armies of Hel and the Frost Jötunn will arrive. After this they will enter into battle where Surtr will kill Freyr. After their battle his fire will engulf the world.