czar vs oligarch

czar

noun
  • An appointed official tasked to regulate or oversee a specific area. 

oligarch

noun
  • A member of an oligarchy; someone who is part of a small group that runs a country. 

  • A very wealthy business owner who wields political power. 

  • A protoplanet formed during oligarchic accretion. 

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