The Hound of Azazel
A supernatural hitman, generally a mortal in possession of the Mantle of the Fallen. Azazel and the Fallen use the Hound for a variety of purposes, most notably to slay those who are bound to Hell. Ostensibly, this is done to ensure such warlocks do not compound their evils in an attempt to stave off the inevitable--the so-called Warlock Death Spiral. As the Fallen are beings on ineffable nature, one can only speculate on their true motives.
The most recent Hound of Azazel was Desmond Cairne. Since his death, the position remains open.