Writing bad guys

Just something I tried out this time. Think of a person or a kind of person who is a good guy for you. Someone you'd really trust and who you look up to. Now imagine that person gone bad. Everyone has choices, you know? And just because you start out as a good person doesn't mean you can't mess up. We all do--but of course, some people decide to fix their messups, and some don't. So imagine that good person, only soured, and you'll get a great bad guy.