eminence grise

eminence grise \ay-mee-nahn(t)s-GREEZ\, noun:

a person who wields power or exerts influence behind the scenes

Some might hypothesize that Mr. Kissinger's perpetual re-emergence as eminence grise reflects the tendency of presidents to change their views after taking office and gradually move in Mr. Kissinger's direction.
-- James Mann, The Ghost of the Oval Office, New York Times, October 4, 2002

Considerably less known in the West than his comrades, he prefers the role of eminence grise.
-- They Made a Revolution, Time, November 5, 1968

As his detractors tell it, Bolland is an eminence grise--a postmodern Richelieu or Rasputin, conniving behind the throne.
-- Ginanne Brownell, By What Mysterious Alchemy Do You Turn The 'Harry Pothead' Scandal Into A Public-Relations Master Coup?, Newsweek, January 27, 1998

by 1838, French for "gray eminence"; originally used in French for Pere Joseph, a monk who was Cardinal Richelieu's confidential agent, for the gray habit he wore, in contrast to the Cardinal's red habit