Who is the real bad guy?

In anime, which the two that come to mind being Code Geass and Death Note, the villain is not always clear. The main characters in those two shows come off as a villain. Sometimes the villain their motives are good, it is just they are seen as a villain due to what they are doing. So is the bad guy the one causing the problems believing it is the right choice and someone is trying to stop them? Or is the bad guy the one trying to stop the problem causer despite the fact the problem causer believes they are making the right choice?