despot

/D EH1 S P AH0 T/
noun
  1. 1

    A ruler with absolute power; a tyrant.

  2. 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)

Source: https://en.wiktionary.org/wiki/despot