(n.) One who manipulates.

Rasputin Svengali VIP access agent bad influence big wheel calculator conductor court driver eminence grise engineer five-percenter friend at court functionary good influence gray eminence handler heavyweight hidden hand influence influence peddler influencer ingroup intriguer key kingmaker lobby lobbyist lords of creation machinator man of influence maneuverer open sesame operant operative operator pilot powers that be pressure group runner schemer sinister influence special interests special-interest group steersman strategist tactician the Establishment very important person wheeler-dealer wire-puller