Villains who have been betrayed in some manner or at least feel betrayed, whether it be by another villain trying to gain more power or, a hero or redeemed villain who didn't approve of their plans. Often, this can be the motivation for vengeance.

A betrayed villain is opposed to a traitor, though it is entirely possible for a villain to be both if they both betrayed someone and were betrayed themselves, whether it's by the same or two completely different people.