During the Dawn War, Hell was the realm of a deity remembered today only as the Mourned God. This god’s Exarch was the mighty Angel Asmodeus, a warrior and hero of the war. As the War lingered on, however, Asmodeus began to resent being constantly sent to the front while his god remained behind in safety. Ultimately, he took advantage of the confusion of the war to commit a terrible atrocity. With a host of rebel angels on his side, Asmodeus rose up against his own deity and slew the Mourned God. He consumed the divine spark of the God and became divine himself, claiming Hell as his own.
Horrified, the other gods took immediate steps. They laid siege to Hell and sealed its borders, trapping Asmodeus and his followers inside. What had been a paradise became now a prison, its features and inhabitants becoming reflections of the horror that had been perpetrated within its borders. The angels who had willingly followed Asmodeus in deicide became devils, and Asmodeus himself was cursed with a terrible form. Asmodeus sneered at the punishment of the Gods. Famously, he’s said to have proclaimed, “Better to rule in Hell than to serve in your Heavens.”
Hell has nine layers, each ruled by its own arch-devil. Asmodeus rules from Nessus, the bottom-most layer. There he plots and schemes, manipulating events on Tol through lesser devils, often called to Tol by mortal clerics, wizards, and warlocks. Asmodeus bides his time, waiting for his chance to break free and wreak vengeance on the gods who denied him what he considers his due.