The phrase power behind the throne refers to a person or group that informally exercises the "real" power of an office. In politics, it most commonly refers to a spouse, aide, or advisor of a political leader (often called a "figurehead") who serves as de facto leader, setting policy through influence or manipulation; because of the nature of the concept of a power behind the throne -- a Mediaeval figure of speech referring to the fact that the king's policies could be set by a counselor not seated in the throne but standing behind it -- it may or may not be common knowledge that the political leader is being influenced by someone else.

In American politics, for example, Dick Cheney (R.), the current U.S. Vice President has been characterised by some as being "the power behind the throne" of President George W. Bush (R.); similarly, the current U.S. Senator Hillary Clinton (D., New York) has been accused by some of having been the same during the Presidency of her husband Bill Clinton (D.). One should be careful in evaluating such claims, as political partisans often seek to portray an opponent as incompetent by suggesting that someone else is in fact responsible for his or her successes.

Another, similar term is éminence grise (French: "gray eminence"), a powerful advisor or decision-maker who operates secretly or otherwise unofficially. This phrase originally referred to Cardinal de Richelieu's right hand man, François Joseph du Tremblay, a Capuchin priest who wore gray robes. Because the Cardinal de Richelieu -- the power behind the throne of Louis XIII, King of France -- , as a Catholic cardinal, was styled Son Eminence ("His Eminence"), his alter ego Père Joseph was called l'éminence grise ("the Gray Eminence").