The Collaborative International Dictionary of English v.0.48:

Machinator \Mach"i*na`tor\, n. [L.]
   One who machinates, or forms a scheme with evil designs; a
   plotter or artful schemer. --Glanvill. Sir W. Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

machinator
    n 1: a member of a conspiracy [syn: conspirator,
         coconspirator, plotter, machinator]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "machinator":
   Benedict Arnold, Brutus, Judas, Judas Iscariot, Machiavellian,
   Quisling, archtraitor, behind-the-scenes operator, betrayer,
   calculator, cockatrice, coconspirator, conniver, conspirator,
   conspirer, counterplotter, double agent, double-crosser,
   double-dealer, eminence grise, exploiter, finagler, gamesman,
   gray eminence, informer, intrigant, intriguer, kingmaker,
   logroller, maneuverer, manipulator, operator, opportunist, plotter,
   pork-barrel politician, quisling, rat, schemer, serpent, snake,
   strategist, tactician, timeserver, traitor, treasonist, trimmer,
   turncoat, wheeler-dealer, wire-puller