noun, feminine/e.mi.nɑ̃s ɡʁiz/plural: éminences grises
éminence grise
From éminence + grise, 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.