I knew Inarius long ago - when he was still among the angels. But he grew weary of battling the demons after a time, and he began to secretly conspire with demons in order to forge a peace. The demoness Lilith became his greatest ally in the Hells, and many other demons and angels joined his cause.
After he gained a following, Inarius stole the sacred Worldstone and used it to create and conceal a world he called Sanctuary. Demons and angels alike fled there, and some of them - including Inarius and Lilith - fell in love. Many of these unions resulted in children. They were called the nephalem.
Inarius was alarmed when he realized that the nephalem had the potential to surpass both angels and demons in power. He wished to limit their abilities, but Lilith demanded that they become her army. Their escalating conflict led to Sanctuary's discovery by the demon lords and the Angiris Council.
In the end, Lilith was banished and Inarius was given over to the demons, who have tortured him in the Hells ever since. Most of Inarius's followers were killed; those who remained shared an even darker fate. Despite the tragedy, I believe the nephalem may yet play a part in resolving the Eternal Conflict.