Frank Angel5 books in series
Angel 1: Find Angel! Publisher's Summary
Swift, deadly, and merciless were the raiders who hit the Kansas ranch, and when they rode out, they left behind two men dead and a woman who wouldn’t make it through the night. With a stolen Army payroll in their saddlebags, they ran for the border, and although they covered their back-trail well, someone was on it. He was a man with a gun, determined to hunt every one of them down. His name was Angel, and the name of his game was sudden death.
And so the Justice Department put their best man into the field with one simple instruction. Before he kills every one of them - find Angel!