What fire giant sets the world ablaze at Ragnarok?

The fire giant who sets the world ablaze at Ragnarök is Surtr.

Surtr is a jötunn associated with Muspelheim, the fiery realm of Norse mythology. In the Poetic Edda, he is foretold to advance from the south carrying a brilliantly shining sword. In Snorri Sturluson’s Prose Edda, Surtr leads the forces of Muspell into the final battle at Vígríðr.

Surtr fights Freyr, who lacks the magical sword he once gave to Skírnir, and Freyr falls. After the gods and their enemies destroy one another, Surtr spreads fire over the earth, burning the world. This destruction is not the absolute end: the sources describe a renewed world rising from the sea, with surviving gods and two human survivors, Líf and Lífþrasir.

A common mix-up is confusing Surtr with Ymir, an ancient primordial being, or Loki, who joins the enemies of the gods but is not the figure who burns the world. Marvel’s Surtur is based on this mythological fire giant.