This guy has been doing evil and or immoral crap his whole life, and for the most part he's gotten away with it. He's more than okay with the occasional murder (or in some rare cases, genocide) so long as he gets what he wants.
But then, one day, something big happens to him. Usually he survives some sort of a murder or assassination attempt. Instead of simply developing a new respect for life and just changing his ways, he flies over to the complete other side of the spectrum, believing that his salvation came at the hands of none other than God himself. Because of this, the (usually self-important) person becomes a preacher or a "messenger of god", undoubtedly gaining devoted followers. The movement typically begins on the fringes of society before moving in as word of the "prophet" spreads.
- Gaius Baltar on Battlestar Galactica (Reimagined) who, after indirectly causing the almost complete annihilation of the human race and subsequently just being kind of a dick, becomes the leader of a fairly fanatical religious sect.
- Boyd Crowder on Justified (for a time). Boyd finds religion after taking a bullet to the chest from Raylan Givens and, upon his release begins to gain followers. Mostly made up of ex-convicts and wanted men, his followers are incredibly devoted to him.