Well before the events depicted in Blizzard's forthcoming Diablo III, there was a great war between archangels and demons. This short film by Aeon Flux's Peter Chung and Metalocalypse animation house Titmouse, depicts "a fundamental moment in the battle between the High Heavens and the Burning Hells."
Basically, it shows Diablo coming face to face with the archangel Imperius, and the decision of what to do with him afterwards. Also, it is very cool.
"What hope can there be when even the wrath of angels cannot be quenched?"
I don't know! I guess that maybe… this situation calls for a hero.