The current series is ongoing, not a mini.

He's a drug addict, who broke into a lab and drank some unknown (to him) chemicals. The Void is his darker self, and is the scapegoat for all of Robert Reynolds' problems. The Sentry's powers are so great that he can create beings, like the Void, his wife (he killed her before and that's why he was in jail at the beginning of Bendis), his dog, etc.

The angel thing was only ever simile, comparing his power to being god-like.