"Power behind the throne" is a phrase commonly used to refer to an influential person who operates behind the scenes and controls important decisions without publicly assuming authority. There are several synonyms that can be used for this term, including puppet master, mastermind, string-puller, backroom strategist, covert controller, silent influencer, hidden authority, and shadow leader. All of these terms depict the idea of someone who wields significant power in a covert manner and is capable of shaping the actions and decisions of those in visible positions of authority. The use of such synonyms can add color and nuance to written and spoken language, enhancing the power of the message being conveyed.