An éminence grise (French: [eminɑ̃s ɡʁiz], grey eminence) is a powerful decision-maker or advisor who operates "behind the scenes" or in a non-public or unofficial capacity.
This phrase originally referred to François Leclerc du Tremblay, the right-hand man of Cardinal Richelieu. Leclerc was a Capuchin friar who was renowned for his beige robe attire (as beige was termed "grey" in that era.) The title His Eminence is used to address or refer to a Cardinal in the Roman Catholic Church. Although Leclerc never achieved the rank of Cardinal, those around him addressed him as such in deference to the considerable influence this "grey" friar held over "His Eminence the Cardinal".
Leclerc is popularly referred to in several works. Aldous Huxley wrote an English biography of Leclerc entitled Grey Eminence. There is also an 1873 painting by Jean-Léon Gérôme, L'Éminence Grise, which depicts him descending the grand staircase of the Palais Cardinal. Leclerc is referred to in Alexandre Dumas' The Three Musketeers as the character Father Joseph, a powerful associate of Richelieu and one to be feared.
An éminence grise can alternatively refer to an elderly ("grey-haired") personage who is renowned for past accomplishments, and now acts as an advisor rather than a principal actor. They might be politically influential as a consequence of their honored status within an influential group or society as a whole. For example, a distinguished retired physics professor emeritus who advises scientific leaders and government officials on nuclear energy; or a retired U.S. Senator who advises the President on an informal basis, etc.
During the George W. Bush administration, Vice President Dick Cheney was viewed as an eminence grise, an "intellectual godfather" of the administration's attempted expansion of presidential powers and its aggressive foreign policy, as well as its perceived Machiavellian view of the world. Said Lawrence Wilkerson, a Cheney critic and one-time chief of staff to Secretary of State Colin Powell: "The power behind the throne — an eminence grise — that's what Dick Cheney has become. The real president of the United States is Dick Cheney." Other common candidates for the title of éminence grise in American political life over the decades have included 
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- Historical reference to address in the Roman Catholic Church
- Mould, Michael (2011). The Routledge Dictionary of Cultural References in Modern French. New York: Taylor & Francis. p. 149. ISBN 978-1-136-82573-6. Retrieved 15 June 2012.
- Walsh, Kenneth T. (January 23, 2006). "The Cheney Factor: How the scars of public life shaped the vice president's unyielding view of executive power". U.S. News & World Report. Archived from the original on January 17, 2006.
- O'Connell, D.P. (1968). Richelieu. New York: The World Publishing Company.