Weigraf Folles from Final Fantasy Tactics.
Probably the best character from that game that can't truly be called a "main character". A man who fights for his country during its time of need only to get thrown to the wolves when he's finished bleeding for it. In return, he tries to stand up to the regime that tossed him aside and instead becomes the very thing he hates by doing do; A perfect example of "He who fights monsters, etc...".
I thought he was a great and well-characterized persona from the get-go, but having served in the military and subsequently been treated poorly by it since then (despite nabbing my honorable discharge), I've come to relate to him on a few more levels. Hell, even when he becomes corrupted, I still find myself agreeing with him (but that's only because I'm a pretty twisted person to begin with).
Can't relate to the dead sister motivation, though.