In Norse mythology’s Ragnarok, the fire giant Surtr sets the world ablaze with his flaming sword. Surtr is a ruler or guardian associated with Muspelheim, the fiery realm, and leads the fire beings against the gods.
The mythic texts describe Surtr crossing into the gods’ world and fighting Freyr. Surtr kills Freyr, who lacks his usual magical sword, and then fire spreads across the world. The sword is often described in translations as bright, shining, or flaming.
Muspelheim is the realm, while Surtr is the named giant. That distinction matters because some retellings use “Muspel” as though it were a person. Surtr is also separate from Hrym, a giant associated with the ship Naglfar in accounts of Ragnarok.