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.

The original concept of a power behind the throne was a Mediaeval-era 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- perhaps whispering in the king's ear- out of common sight.

Good historical examples of a "power behind the throne" include General Hideki Tojo of Japan, who was influential in the military's actions leading up to World War II and later became Prime Minister of Japan in 1941. He served under Emperor Hirohito, who ruled as a deified figurehead. Another example is the rule of Pol Pot in Cambodia from 1975-1978, who led the Khmer Rouge to victory following a devastating civil war. King Norodom Sihanouk returned to reign over Cambodia, but held no executive power.

More modern examples of a "power behind the throne" exist as well, albeit in a more partisan and ambiguous sense. In American politics, for example, Dick Cheney, the current U.S. Vice President has been characterized by several Democrats as being "the power behind the throne" of President George W. Bush; similarly, the current U.S. Senator Hillary Clinton was mocked by several Republicans as having played the same role during the Presidency of her husband Bill Clinton, particularly with his failed healthcare plan, dubbed Hillarycare by critics.

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 Leclerc du Tremblay, a Capuchin priest who wore grey 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 (meaning "Grey Eminence," which is also the English title of his biography by Aldous Huxley).