Múspellson is the Old Norse word for “Son of Muspell” (essentially a Fire Giant), Múspellsynir is plural. The lore of the Germanic religions heavily featured giants (Eutens – Anglo-Saxon, Etunaz – Proto Germanic, Jötnar – Old Norse), and they were generally seen as personifications of strong natural forces, though separate from the gods. Of the various races, the Múspellsynir are one of the least attested. While several tales in the Eddas and other historical Norse sources involve Jötnar or Hrímþursar (Frost Giants), only a single figure is identified as a Múspellson. The role of the Fire Giants is very specific in Norse mythology: they are the destroyers of the universe at Ragnarök (Doom of the Gods). However, to understand them, one must understand where they come from.
In the Old Norse cosmology of Nine Worlds, the Fire Giants were believed to dwell in Múspellsheimr (Home of Primordial Flame) – or simply Múspell – one of the eldest realms. It was said to be a volcanic world far to the South, whose fires extended in ancient times and mixed with the ice of northern Niflheimr (Home of Mist) to create water, and thus all life. The name Múspell itself is derived from the Old High German term Mūspilli which appears in a 9th-century poem by the same title, describing the end of the world. The word Mūdspelli in Anglo-Saxon also denotes a similar thing, and is found in the poem Heliand. Immediately, parallels can be drawn between the domain of the Múspellsynir and their contribution to the Norse equivalent, Ragnarök.
Unfortunately, few details are given about the Fire Giants’ appearance or culture. As their primary function in mythology is to wreak destruction upon the Nine Worlds by engulfing them in fire, it could be assumed that they are a fierce warrior race. Their leader is Surtr (Surt) whose name means the “Black” or “Swarthy One”, and may allude to charred or leathery skin. In addition, he is considered the personification of volcanic activity, something that would have been historically important to the people of Iceland. The Prose Edda also mentions that during the final battles of Ragnarök, the weapons and armour of the Múspellsynir shine brilliantly, and Surtr’s own flaming sword is described as being “brighter than the sun”. However, other than Surtr, there are none who can be irrefutably distinguished as an Múspellson, though a few bear their traits. For example, some texts list the giantess Sinmara as his consort, while one tale involving an eating contest between Loki and the giant Logi suggests the latter is an embodiment of fire. The Múspellsynir were nevertheless pivotal to Old Norse religion, and remain an interesting aspect of it.