Tyrant
originally, one who obtained supreme or absolute power by usurpation, or who derived it from one who had obtained such power by usurpation, and maintained it by force, though he might exercise his power with strict moderation. Specifically, a monarch, or other ruler or governor, who takes advantage of his power to oppress his subjects or fellow citizens; one who exercises unlawful authority, or legal authority in an unlawful manner; one who acts toward those who are subordinate to him in a manner which law and humanity do not authorize, or which the purposes of government or policy do not require; a despot; a cruel task master; an oppressor.