The phrase "power behind the throne" refers to a person or group that informally exercises the real power of a high-ranking office, such as a head of state. In politics, it most commonly refers to a spouse, aide, or nominal subordinate of a political leader (often called a "figurehead") who serves as de facto leader, setting policy through possessing great influence and/or skillful manipulation.
The original concept of a power behind the throne was a Medieval-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. Among the earliest examples of such powerful advisors were the Mayors of the Palace under the Merovingian kings.
Historical examples of a "power behind the throne" include: Nogai Khan, Mamai and Edigu in the Golden Horde; Diego Portales of Chile; Chancellor of Germany and Minister President of Prussia Otto von Bismarck, with German Emperor and King of Prussia William I as a de facto figurehead; Martin Bormann of Nazi Germany.
The Genrō had this role in Meji period of Japan.
Another example is the rule of Pol Pot in Cambodia from 1975-78, 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.
In the United States, Edith Wilson – the second wife of President Woodrow Wilson – took over many of the routine duties and details of the government after her husband had been incapacitated by a stroke. Another modern example was Deng Xiaoping in China, who was recognized as China's paramount leader without holding the position of either General Secretary or President.
Much earlier examples that come to mind, are the magistri militum of the later decades of the Western Roman Empire. Examples of such are Stilicho the general of Emperor Honorius, Aetius, the power behind the throne of Honorius' nephew Valentinian III, Ricimer the puppet master of Emperors Avitus, Majorian, Libius Severus, Procopius Anthemius and Olybrius, and then finally Flavius Orestes, the father of the usurper emperor Romulus Augustulus, and the Germanic chieftain Odoacer, who were the masters in the West during the reigns of Emperor Julius Nepos and then Orestes' son, the aforementioned Romulus. Odoacer then deposed the figurehead Roman ruler, captured and executed Orestes, and established his own Italian kingdom as the Dux Italiae, only to be overthrown by the Ostrogothic chieftain Theodoric on the behest of the Eastern Emperor Zeno.
In Latin America, a good example was Joseph-Marie Córdoba Montoya during the Presidency of Carlos Salinas de Gortari (1988–1994). Córdoba Montoya, a French naturalized Mexican, was the Head of the Office of the Presidency, and was considered the second-most powerful man in Mexico at the time. Another example in the same region is the one of the former general Manuel Noriega, who was the military leader and the de facto chief of state of Panama from 1983 to 1989.
A related 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 (also known as the Père Joseph), a Capuchin friar who wore grey robes. Because the Cardinal de Richelieu, the power behind the throne of King Louis XIII of France, as a Catholic cardinal was styled Son Eminence ("His Eminence"), his alter ego Père Joseph was called l'éminence grise (which is also the English title of his biography by Aldous Huxley). Martin Bormann was referred to as the Brown Eminence, brown referring to the brown uniform of the Nazi Party.
The modern usage of the term Proconsul, as analogy for a person from a foreign power manipulating another country's internal affairs, is also referred as the power behind the throne.