usurper Meaning, Definition & Usage

  1. noun one who wrongfully or illegally seizes and holds the place of another
    supplanter.

WordNet

U*surp"er noun
Definitions
  1. One who usurps; especially, one who seizes illegally on sovereign power; as, the usurper of a throne, of power, or of the rights of a patron.
    A crown will not want pretenders to claim it, not usurpers, if their power serves them, to possess it. South.

Webster 1913