counterpart vs poster child

counterpart

noun
  • One who or that which has corresponding functions or characteristics. 

  • Either of two parts that fit together, or complement one another. 

  • One who or that which resembles another. 

  • A duplicate of a legal document. 

  • Either half of a flattened fossil when the rock has split along the plane of the fossil. 

verb
  • To counterbalance. 

poster child

noun
  • One who is a prototypical or quintessential example of something. 

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