(ש"ע) מסית, ממריץ, מגרה, משסה

n. inciter, one who urges or prods, agitator, one who stimulates

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Noun
1. someone who deliberately foments trouble; "she was the instigator of their quarrel"
(synonym) provoker, inciter, instigant, firebrand
(hypernym) troublemaker, trouble maker, troubler, mischief-maker, bad hat
(hyponym) ringleader
(derivation) incite, instigate, set off, stir up
2. a person who initiates a course of action
(synonym) initiator
(hypernym) leader
(hyponym) aggressor
(derivation) prompt, inspire, instigate

(n.)
One who instigates or incites.
  

instigator