Despot

Noun

 * 1) A ruler with absolute power; a tyrant.
 * 2) A title awarded to senior members of the imperial family in the late Byzantine Empire, and claimed by various independent or semi-autonomous rulers in the Balkans (12th to 15th centuries)

Thesaurus
absolute monarch, absolute ruler, all-powerful ruler, arrogator, autarch, autocrat, caesar, commissar, czar, dictator, disciplinarian, driver, duce, hard master, martinet, oligarch, oppressor, pharaoh, slave driver, stickler, strong man, tyrant, usurper, warlord