In Diablo 4, more so than any other game in the series, the world in which the Diablo universe is set, Sanctuary, is almost a character with a full backstory and personality all its own.
There's both Diablo Immortal and Diablo 4 guaranteed on the horizon, with a potential revisiting of Diablo 2's story in a remastered (nay, Resurrected?) version.
The demons of the Burning Hells have the Greater and Lesser Evils, but those seven dark eminences agreed on almost nothing, and as a result, the Hells have almost never been united to a singular purpose.
Before the coming of the Nephalem, Imperius was the unquestioned greatest warrior in all creation.
In his time, he has served as the Archangel of Justice and sat as Wisdom on the Angiris Council.