Well, long before Robert Reynolds was born, the Void brought the divine plagues down on Egypt and Osborn says that the Void is the Angel of Death.

IMO, the best suspect is Abaddon/Apollyon/Exterminans/Abbaton, the Destroyer, the Angel of the Abyss.
http://en.wikipedia.org/wiki/Abaddon

If Abaddon had needed an host, Robert Reynolds would have been the perfect choice thanks to his self-destructive behaviour.

Rev. 9:10-11 "And they had tails like unto scorpions, and there were stings in their tails: and their power was to hurt men five months. And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon."

This portrayal fits with the monstrous form seen in the Siege comic book.