The phrase "grey eminence" is often used to describe a powerful person who operates in the background, pulling strings and exerting influence without drawing too much attention to themselves. Synonyms for this term might include "power broker," "kingmaker," "shadow politician," or "behind-the-scenes operator." Other variations on the theme could include "puppet master," "mastermind," or "manipulator." Depending on the context, some other options might be "elusive figure," "secret advisor," or "hidden hand." Regardless of their title or nickname, these figures tend to be highly respected and feared by those who understand the extent of their power and reach.