éminence grise
/ˌɛmɪnɒ̃s ˈɡriːz
/noun (plural éminences grises pronounced same)
A person who exercises power or influence in a certain sphere without holding an official position: for years he has been an éminence grise operating in the shadows of party policy-making...
- But the Hutton inquiry isn't the kind of thing that éminences grises and powers behind thrones are used to.
Origin
1930s: French, literally 'grey eminence'. The term was originally applied to Cardinal Richelieu's grey-cloaked private secretary, Père Joseph (1577–1638).