The Collaborative International Dictionary of English v.0.48:

Manipulator \Ma*nip"u*la`tor\, n.
   One who manipulates, sometimes in an underhanded or
   fraudulent manner; as, a stock market manipulator.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

manipulator
    n 1: an agent that operates some apparatus or machine; "the
         operator of the switchboard" [syn: operator,
         manipulator]
    2: a person who handles things manually

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "manipulator":
   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