An unlikely chemical capable of tapping into that same power that caused the Ten Plagues of Egypt – i.e. the Wrath of God – Sentry Serum was created by a un-named Professor in an attempt to recreate the Super Soldier Serum.
Clearly, he succeeded beyond his wildest dreams. Just as clearly, the addict and thief who took the sole, untested sample of the serum, Robert Reynolds, was manifestly unsuited for the nigh-infinite power it unleashed in him.
It is unclear whether the serum caused his multiple personalities, or merely exacerbated an existing tendency in Reynolds, but in either identity – the ‘heroic’ Sentry or the evil ‘Void’ – he had more power than he could easily control. With his death, it is unlikely that the serum will ever be recreated.