(n.) One who machinates, or forms a scheme with evil designs; a plotter or artful schemer.

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