The Vengeance Seeker by Will C. Knott (Wolf Caulder Series, Book 1) from Books In Motion.com

He had a reason for living: to kill When he was just a boy, the five saddle tramps had murdered his parents in front of him, and nearly beaten him to death. Rescued by a kindly old Spaniard, most of Wolf's physical wounds were healed. They took his eye, his childhood and his parents, and now Wolf would show them vengeance. For ten years he plotted as he grew, and sharpened his skill with his Winchester rifle and Colt revolver. Then he went after them, one by one.