ém·i·nence grise 
(ā-mē-näɴs grēz)
(ā-mē-näɴs grēz)n. pl. ém·i·nence grises (ā-mē-näɴs grēz)
A powerful adviser or decision maker who operates secretly or unofficially. Also called gray eminence.
[French, the power behind the throne : éminence, power + grise, feminine of gris, gray, shadowy.]