Vindictator

Vindictator: noun. A person who claims absolute power over a piece of land or community of people on the basis of being wronged before. It isn't really important whether the vindictator was wronged by the specific group of people he or she is ruling. In fact, it is more desirable for the vindictator to be wronged by someone completely unconnected, as he or she will feel less compelled to randomly take revenge on his or her subjects.