If its normal in your comic to use real world literary references you could call him an Iago. Judas is another, more Biblical reference.
Some terms are usurper, snake, turncoat, deceiver, intriguer, backstabber, imposter, treasonist, schemer, manipulator, conspirator, plotter, whisperer, tempter (temptress), seducer, enticer, coaxer, siren, wolf-in-sheep's-clothing, trickster, charlatan, fraud, pretender, sophist, swindler, con artist, two-faced, double-crosser, masquerader, conniver, hypocrite, pharisee.
Haha in my head I kept thinking of the Poke-Rap as I started reading them out.
