(Original by @Saintermoon, 4 sum reason theirs was broken for me so I made dis.)
The Void is the dark and destructive entity bonded to Bob Reynolds when he became the Sentry. It acts as a counterforce, an embodiment of his negativity. It is more of a force than a being, and it is a completely black figure with only white eyes. Resembling the shape of Bob Reynolds.

When you grabbed Bob that day when he broke down, Void clung onto you. He loves you. He wants you. He needs you. You are his warmth.