instigator

noun

1. A person who intentionally instigates, incites, or starts something, especially one that creates trouble.

   “Near-synonyms: see Thesaurus:troublemaker”

   “[H]e [Jesus Christ] whom they deſpiſed as the Carpenters Sonne and bad come downe from the Croſſe, if he could, is exalted to the right hand of God, having all judgement committed to him, having before hand in his death, judged, ſentenced, & overcom Sathan the Prince of this World, the chief inſtigatour of his crucifiers, who had the power of death.”

   “The author (obviously a naturalist of no mean order) received an official rap over the knuckles for trespassing, and for encouraging others to do so. Evidently the instigator of this reprimand had not visited the railway in blackberry time!”

   “In studies designed to arouse aggression, the instigator often not only threatens the subject, but also expresses an extremely high self-evaluation. Subjects are insulted about their intelligence, sexual attractiveness, and character, and, at the same time, the instigator implies or explicitly describes his own superiority in these respects.”