power behind the throne; éminence grise; kingmaker; wire-puller; shadow shogun
Refers to a person who wields real power from behind the scenes, often in politics or organizations, without holding an official top position. The literal meaning is 'shadow shogun'.
He is said to be manipulating the political world behind the scenes as a shadow shogun.
その会社の真の支配者は、表に出ない闇将軍だ。
The true ruler of that company is a behind-the-scenes power broker who never appears in public.