The Collaborative International Dictionary of English v.0.48:
instigant \instigant\ n. one who instigates; someone who deliberately provokes trouble; an instigator. Syn: instigator, provoker, inciter. [WordNet 1.5]WordNet (r) 3.0 (2006):
instigant n 1: someone who deliberately foments trouble; "she was the instigator of their quarrel" [syn: instigator, provoker, inciter, instigant, firebrand]