Múspellsheimr's role in the creation comes from Snorri's Gylfaginning. Its role at Ragnarök is described in Völuspá and Gylfaginning. Surtr appears in both. The word múspell is etymologically obscure and may be very old — possibly pre-Norse.
The Other Primordial Realm
Múspellsheimr stood opposite Niflheim across the void of Ginnungagap. Where Niflheim was cold, dark, and misty, Múspellsheimr was blazing, bright, and impassable to those not native to it. Its sparks and embers flew northward into the void, meeting the ice of Niflheim's rivers, melting them, creating the drips from which Ymir formed.
Múspellsheimr did not participate in the creation of the world the way Niflheim did — its contribution was passive, its heat doing the work of melting. But it is not neutral in the cosmos. At Ragnarök, its role is active and total.
The word múspell is one of the most debated in Norse scholarship. It appears in Old High German as mūspilli — in a Christian poem about the end of the world, describing the fire of judgment. The word may be pre-Christian and pre-Norse, a term for world-ending fire that Germanic peoples carried from very early periods and applied to both their mythological and (later) Christian end-time concepts. Its etymology is not settled. Its antiquity appears genuine.
Surtr — The One Who Waits
Surtr (the black one, or the scorched one — svartr, black) rules Múspellsheimr. He stands at its border with a flaming sword, guarding against intrusion. He is described as "the first" — not the first being created, but the first in Múspellsheimr, the one who has been there from the beginning. He is not the fire itself; he is the being who commands it.
At Ragnarök: the sons of Múspell — Surtr's forces — ride north and break Bifröst under their weight. They cross the now-broken bridge and reach the field of Vígríðr, where the final battle takes place. Freyr meets Surtr there and dies — because Freyr gave away the sword that fights giants on its own, the one weapon that might have matched Surtr's flame. Freyr fights with an antler and is killed.
After the battle, Surtr throws fire over the nine worlds. Everything burns. The earth sinks into the sea. The stars fall. Everything that was made from Ymir's body returns to formlessness. The fire that was present at the creation of the world — as scattered sparks from Múspellsheimr — is present at its end, now as consuming conflagration.
Then: a new earth rises from the sea. The surviving gods meet. Some of the dead return. A new cycle begins. Surtr's fire was not the end; it was the clearing.
Fire as Cosmological Principle
Fire in Norse cosmology is not simply destructive — it is the other half of the creative principle. The world was made from the meeting of ice and fire. The world ends in fire. A new world emerges after. The Norse cosmological cycle is not linear (creation → existence → destruction) but something closer to a breath: the universe exhales into existence, burns to ash, and inhales again into a new form.
Surtr is not evil in the moral sense. He is the fire principle, doing what fire does: consuming what exists to clear space for what comes next. The Norse did not require their apocalyptic figures to be villains. They required them to be inevitable.