Sometimes life as you know it has to nearly end for you to find your true calling. By "end" I mean the everything you knew, loved, and held dear ripped away, your life torn down to the bloody roots and dragged over broken glass until the future yawns like a great big empty pit that threatens to swallow you whole type of ending.
The new you, the one that's left after such a sundering, is someone the old you would probably put a bullet in the brain pan of out of sheer mercy. Problem is, the old you is no longer around, and the new you likely doesn't have anyone left that cares enough to administer that hollow point piece of mercy.
An ex-cop vigilante, suitable for modern day supernatural horror settings.