éminence grise

 
Syllabification:
Pronunciation: /āmēnäNs ˈgrēz/

noun (plural éminences grises pronunc. )

  • a person who exercises power or influence in a certain sphere without holding an official position.

Origin:

1930s: French, literally 'gray eminence'. The term was originally applied to Cardinal Richelieu's gray-cloaked private secretary, Père Joseph (1577–1638)