(n.) One who forms schemes; a projector; esp., a plotter; an intriguer.

Benedict Arnold Brutus Judas Judas Iscariot Machiavellian Quisling archtraitor betrayer calculator cockatrice coconspirator conniver conspirator conspirer counterplotter double agent double-crosser double-dealer exploiter finagler informer intrigant intriguer machinator maneuverer manipulator operator opportunist plotter quisling rat serpent snake strategist tactician timeserver traitor treasonist trimmer turncoat wire-puller