Thor was caught by the Fire Demons Lord, Surtur, in Muspelheim. Thor managed to escape with the help of Mjølnir, so Surtur summoned his Fire Demons to kill him. Thor defeated the demons with a powerful blast of lighting. With having most of the demons gone, Thor killed Surtur and took his crown back to Asgard.
- The Fire Demons are loosely based on the Fire Giants of Norse Mythology. In the comics, they were the offspring of Surtur and entirely made of flames.
- In the non canon videogame Thor: God of Thunder, the Fire Demons and the Frost Giants launched an attack on Asgard, but were defeated by the Asgardians.