Slain in the war that brought about the fall of his father, Ahriman's spirit stayed in the mortal realms, manifesting as a shapeless cloud of utter darkness with two red glowing eyes. He was known as a demon to the elves from ancient times to the fall of their empire, and was consulted by great wizards and sages.
After the War of Tears he was cast down by the new demons and imprisoned in a magical tomb, fashioned from a block of obsidian and hidden deep within the Dragonspine Mountains near the area of present day Foxcourt. A second piece of obsidian, shaped like a large egg, formed the key to the tomb and that was cast into the aether, coming to rest in the plane of Empyrea.
During the thousands of years after the War of Tears the tomb under the mountains leaked some of Ahriman's power, which seeped into the rocks to form Warpstone, the effects of which warped and twisted the dwarven miners who lived in the area Kheledgundu turning them into Dark Dwarves. The tomb was located by one of Baal's balrog servants named Garthron who took it upon himself to protect the tomb, and to one day free his master. In the meantime he nurtured the dwarvs, and taught them that Ahriman was their sleeping god, (and Garthron his servant). He gained the chance to release Ahriman when in 789 WK a Guild party ventured into the area and Garthron gave them the task of finding the key to his master's tomb (on pain of his considerable displeasure).
While Ahriman remained trapped in his tomb, two avatars had manifested in Empyrea, the controlling, ambitious and power hungry being known as The One, and the kindly arch-mage Doc, champion of the free peoples of Empyrea. Both felt compelled to influence events on Empyrea, touching off many wars over the millenia. Thirty years ago, The One, helped a dark lord named Krelloc into power and slowly beat back the free Emypreans. In 790 WK a Guild party procured the key to the tomb and returned to Alusia freed Ahriman. With Ahriman's release both Doc and The One vanished.
The Ahriman who was released however was a very different being to the one who had been trapped. Thousands of years of contact with mortals on Empyrea, and seeing (and causing) both sides of the struggle between tyranny and freedom had changed Ahriman considerably.
Thanking the party for their assistance, he dismissed Garthron, and disappeared into the dark under the mountains with his dwarven followers.
Ahriman resurfaced after the release of his brother Apollyon, and it became known that he opposed Apollyon's plans to release their father Baal, and bring about the destruction of Alusia. He also became involved in local situations sending some 500 of his heavily armed and armoured Dark Dwarves to join alliance forces against the Dark Circle. Over in Terranova Ahriman's forces, bolstered by local primitive dwarves fought a bitter underground battle against Apollyon's northern army who were attempting to breach the hills surrounding the central Drow lands and drive towards the city of Kadath.
It also came to light that under the same Red Hills in Terranova Ahriman's local minions had for thousands of years been tending enormous reservoirs, a dark graal containing the waters that would one day revitalise that arid land. This great work appears to have been a favour or obligation that Ahriman was discharging to Xanadu the dragon-father.
Apollyon's forces finally pushed through the hills, though it is believed that Ahriman may have guided their exact route in line with his eventual plan. Apollyon's forces flooded the sea of silt in the central Drow lands, and attacked Kadath which was defended by the armies of the Ruby Scourge, assisted by Ahriman, and elementals working for Istu. In the climatic battle for the city, Ahriman's forces withdrew, and Istu's elementals undermined the crags surrounding Kadath (which they had been defending), causing Apollyon's floodwaters to surge into the volcanic area around the city. A vast explosion obilterated Apollyon's army, and destroyed the city.
With the release of Baal and his subsequent departure with most of the remaining Ancient Dragons from mortal realms, Ahriman is believed to be back working with his dwarven followers, and now reunited with his wife from the ancient days, Eriskigal.
His (and her) current whereabouts are not known.