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Grey Eminence: A Study in Religion and Politics is a book by Aldous Huxley published in 1941. It is a biography of François Leclerc du Tremblay, the French monk who served as advisor to Cardinal de Richelieu. He was also known as Father Joseph and as l'éminence grise; that phrase originally referred to du Tremblay.
Political and economic commentator David P. Goldman called this book "[t]he best book on the intelligence operations of the French state" during the Thirty Years' War.