éminence grise
"éminence grise" (literally, "gray eminence") was the sobriquet of Père Joseph (1577–1638), the Capuchin monk who served as secretary to Cardinal Richelieu, Chief Minister under Louis XIII. Richelieu's ambition for French domination of Europe aligned neatly with Joseph's hope to convert European Protestants to Roman Catholicism. Joseph's nickname came from the color of his cloak—and from the fact that Richelieu himself was known as the Éminence Rouge (Red Eminence). The term "éminence grise" came to mean a loyal confidant of any powerful individual, but recently the word has alternately come to mean a respected senior member within a field or profession (the gray in this case perhaps alluding to the color of an elder's hair)."