provocateur

from WordNet (r) 3.0 (2006)

provocateur
    n 1: a secret agent who incites suspected persons to commit
         illegal acts [syn: {agent provocateur}, {provocateur}]

from Moby Thesaurus II by Grady Ward, 1.0

21 Moby Thesaurus words for "provocateur":
      agent provocateur, agitator, agitprop, catalyst, demagogue,
      exciter, firebrand, fomenter, incendiary, inciter, inflamer,
      instigator, mischief-maker, provoker, rabble-rouser, ringleader,
      rouser, seditionary, seditionist, troublemaker, urger