whoever vs whomever

whoever

pron
  • Any person or persons. 

  • Any person or persons that. 

  • Who ever: an emphatic form of who. 

  • Regardless of the person or persons that. 

  • The person that (no matter who). 

whomever

pron
  • Whatever person or persons (as object of verb or preposition). 

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