I don't know if you have any interest at all in reading manga, but if you do, you should check out Death Note as the central theme is someone doing evil in the name of good, and becoming increasingly corrupted as the series goes on. It starts with a high school boy, Light, who finds this notebook that will kill anyone whose name he writes in it. He starts using it to kill criminals, wanting a world where no crime exists. It's one of my favorite series and just really interesting because you don't often see a protagonist like that.