There are lots of great answers ranging back to Liu Pengli in 2nd century B.C. China. Who was deposed as a prince for hunting his own people for sport. And his story is just the beginning the tales only get um... juicier? from there. Cannibalism, rape, poison, torture, conspiracies, werewolves, vampires, weird experiments, we have records of hundreds of serial killers throughout history and there are probably thousands more we don't know about.

Check out this previous thread and I also recommend you visit Wikipedia From the phrasing of your question I think you'll find what you are looking for best in those links. If you want more information on a particular individual or case I suggest you post a more specific question.