This is not official, but an interpretation by Diablofans forum members: Atrumentis and Daemaro, based on the description of Angel Imperius from the Diablo: The Sin War Trilogy pocket book by Richard A. Knaak. The Diablo III artwork that may be found at the official Diablo III website shows an angel with a peculiar bright sword on his chest.
Here is an excerpt from Book three: The Veiled Prophet:
“THERE IS NO NEED FOR THIS DEBATE TO CONTINUE … OR TO HAVE EVEN BEGUN, declared a majestic angel with robes of royal red and a shining breastplate upon which the image of an upturned sword blazed.
It is not known who the angel in the image below is, but we do have clues that Diablo: The Sin War trilogy is canon lore that serves as ground for the development of the Diablo III Single Player. Angel Imperius is one of the five members of the Angiris Council in the High Heavens. Share your thoughts at the DiabloFans forums.