Usurper
Pronunciation : U*surp"er
Part of Speech : n.
Definition : Defn: 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.
Source : Webster's Unabridged Dictionary, 1913