an absolute ruler, esp. a monarch who holds and exercises the powers of government as by inherent right, not subject to restrictions.

a person invested with or claiming to exercise absolute authority.

a person who behaves in an authoritarian manner; a domineering person.

noun

authoritarian , caesar * , despot , fascist , hitler , overlord , totalitarian , tyrant , dictator , martinet , czar , mogul , monarch , ruler , sovereign , tsar , tzar