éminence grise

Borrowed from French éminence grise (literally “grey eminence”), originally applied to François Leclerc du Tremblay (1577–1638), also known as Père Joseph, a French Capuchin friar who was the confidant and agent of Cardinal Richelieu (1585–1642), the chief minister of France under Louis XIII (1601–1643). The term refers to du Tremblay’s influence over the Cardinal (who bore the honorific of Eminence), and the colour of his habit (grey, rather than the red of a cardinal).

• "But Harry Hopkins was no mere manipulator of people and ideas, no eminence grise masterminding the actions of figureheads."
• "[Ichirō] Ozawa is the Secretary-General of [Yukio] Hatoyama's Democratic Party of Japan (DJP) and the éminence grise of the electoral campaign that catapulted the new Prime Minister to power."

• power behind the throne
• gray eminence

• puppet master
• svengali