power behind the throne

/P AW1 ER0 B IH0 HH AY0 N D DH AH0 TH R OW0 N/
noun
  1. 1

    Someone who appears to be without special status, but who has great covert influence on a person in authority.

Source: https://en.wiktionary.org/wiki/power%20behind%20the%20throne