In Norse mythology, Surtr (modern Icelandic Surtur, sometimes Anglicized Surt) is the leader of the fire giants in the south, the ruler of Muspelheim, the realm of fire. His name means "Swart" or Black, and at the end of the world, Ragnarok, his hordes will rush north like a south wind to overwhelm the gods.

In Snorri Sturluson's Edda (1179-1241): "Surtur is the one so named who stands on Múspell's border, guarding the land. His sword is flaming and as the world ends he will go out, make war against and triumph over the gods. And he will burn the whole world with fire" (Gimlé Gylfaginning, iv). Only Hodmimir's Forest will remain, because that is the only thing his sword can not destroy. He will kill the unarmed god Freyr as well.

Surtsey is a new volcanic island that surfaced off the south coast of Iceland in 1963. Its name in Icelandic means "Surtur's Island".

In the final battle, Surtr and his Fire-Giants burst forth: "In Surtur's grasp the Sword of Revenge blazes, adding a blood red colour to the twilight of the whole world."

At the end of the gods and the world, as it is said in the Völuspá:

Surtur from the south
Wielding fire
The gods' swords shine in the darkness,
like stars in the night
Mountains collapse into rubble
And fiends shall fall
Man walks the road to ruin
as the sky splits in two