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.
Surtr means "Swart" or Black.
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).
At the end of the world, Ragnarok, Surtur's hordes of fire giants will rush north like a south wind to overwhelm Asgard: "In Surtur's grasp the Sword of Revenge blazes, adding a blood red colour to the twilight of the whole world.". Surtur is the being who cleanses Asgard with fire after all the gods have fallen in battle at Ragnarok, the periodic destruction of Asgard. Only Hodmimir's Forest will remain, because that is the only thing his sword can not destroy. Surtur will kill the unarmed god Freyr among others.
At the end of the gods and the world, as it is said in Völuspá:
"Surtur from the south
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"
- Surtr is, under the name of Surtur, a semi-recurring villain in the Marvel comic-book The Mighty Thor.
- In the Dungeons & Dragons roleplaying game, Surtr is the god of fire giants.
- Surtur was also featured in the webcomic The Order of the Stick. 
- Swedish death metal band Amon Amarth has a song titled "Releasing Surtr's Fire"
- In the science-fiction series Starcraft, the Surtur brood is a heavy support force of the Zerg Swarm.
- Surtur is the final boss in Castle of the Winds.
- Surtr (Named "Surt" in the game) is a possible final boss in the video game Valkyrie Profile: Lenneth and Valkyrie Profile
- In Playstation 2 game Shin Megami Tensei: Nocturne, Surt is one of three bosses in the Diet Building.
- In Persona 3, Surt is a Persona the player can obtain after maxing out the Magician Social Link. It is the strongest Persona of the Magician Arcana.
- In David Lindsay's novel A Voyage to Arcturus, the protagonists travel to a planet of that star to seek a being called Surtur.
- The Pagans MC patch depicts Surt wielding a flaming sword, plus the word "Pagans" in red, white and blue.