A manipulator or otherwise generally corrupt person who "games" a system, group of people, or other entity for selfish gains; especially of a political "sell-out" perceived as lacking integrity.
A con artist; someone who pulls confidence games; a swindler, scammer, huckster, hustler, and/or charlatan.
An individual person who acts on his or her own initiative, without partners, especially one who has sole responsibility for doing something questionable, confidential, or iniquitous.