The way he acts so hateful and obsessed, he has to have a reason besides the fact that he used to be a vigilant.

I think the Silver Hand had less contempt for Werewolves than he does for vampires.

So there has to be something in his past. Like maybe a vampire murdered his family, or turned the woman he loved into one and then flew off into the moonlight with her, or something like that.

I like to imagine this too. And add in the part he might have gotten chomped on and barely survived. Now there's alot of deep-seated vendetta going on, or something like that.