Surtr (Old Norse: Surtr, meaning ‘Black’ or ‘Swarthy’) is the fire giant who guards the realm of Múspellsheim and who will lead the assault on the gods at Ragnarök, wielding a flaming sword brighter than the sun. He is one of the most clearly defined eschatological figures in the Norse primary sources, attested consistently across Völuspá, Gylfaginning, and Vafþrúðnismál.

At Ragnarök, Surtr kills the god Freyr — a detail consistent across Völuspá (st. 52) and Gylfaginning, and directly connected to the mythological episode in which Freyr gave his self-fighting sword to his servant Skírnir, leaving him weaponless against the fire giant. After the destruction of the gods, Surtr engulfs the entire world in fire — Völuspá describes the earth sinking into the sea as flames leap to the sky.

Surtr is described in Gylfaginning as already existing at the beginning of time — present at the southern edge of creation from its earliest moment — making him one of the most primordial beings in the Norse cosmological system.