Éminence grise
An éminence grise (French pronunciation: [eminɑ̃s ɡʁiz]) or gray eminence is a powerful decision-maker or advisor who operates covertly in a non-public or unofficial capacity. Originally, the French expression referred to François Leclerc du Tremblay (Père Joseph), the right-hand man of Cardinal Richelieu, the de facto ruler of France.