Muspelheim

Muspelheim was the home of the knowledge-chasing Eldari race in the Aeon of the Champion story series - now, it serves as the base of operations for the Marching Horde and its demonic activity.

Origins
Muspelheim, a part of the Yggdrassil world-tree group, was blessed by the titans of the Pantheon during the Formation of the Universe, approximately 1 million years ago. It was then added to Yggdrassil, along with Middle-Earth, a matter of years afterwards, during the Ordering (which harmonised the previously-chaotic nature of the Universe). Events now set in motion, the regular-sized mortals reigned on Middle-Earth (or so it was to be). The Eldari, a race of knowledge-seeking humanoids, were instructed by the Aesir themselves in the usage of magic, and from that knowledge they built an illustrious civilisation across the planet. The Triuumvirate of Elders - Balmiszen, Tiz'galath and Vel'naar - supervised the construction of some of the proudest works of the Eldari race. The planet was also kept out of the Sin War as it had not been targeted by the Marching Horde; this is because it was not believed to contain the Fusion Staff's crystals. That being said, the Dark One had other plans for the intelligent inhabitants of the planet.==Fall of Muspelheim== When Sargamon offered the Eldari unimaginable knowledge if they turned their services to him, Balmiszen and Tiz'galath accepted his offer without another thought. Vel'naar did not, and,  taking the sane Eldari with him, fled the planet. Those remaining were transformed into demon warlocks, with Tiz'galath handing Sargamon and his demons the keys to the Eldari's citadels. Balmiszen and Tiz'galath, in the aftermath, became the Dark One's left and right hands respectively.

The planet was subsequent tortured beyond recognition, and morphed into a bubbling cauldron of green, hellish energy.

Trivia

 * Muspelheim is a world in Norse mythology, and oddly enough it is also a fiery realm - though in their texts it is ruled by Surtyr.
 * ​In AoC lore, Surtyr ruled over Jotunheim, along with Lokil.
 * Muspelheim is the AoC counterpart to Argus in Warcraft; the Eredar inhabitants of that world suffered a similar fate to the Eldari.