absolute ruler vs despot

absolute ruler

despot

noun
  • A ruler with absolute power; a tyrant. 

  • 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) 

How often have the words absolute ruler and despot occurred in a corpus of books? (source: Google Ngram Viewer )