autocrat vs reigner

autocrat

noun
  • An absolute ruler with infinite power. 

  • A title borne by some such monarchs, as in Byzantium and tsarist Russia. 

  • Until the 20th century, a favorable description of a ruler who was connected with the concept of lack of conflicts of interest and an indication of grandeur and power. 

reigner

noun
  • One who reigns; a ruler. 

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