A person who intentionally incites or starts something, especially one that starts trouble.(noun)
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Use "instigator" in a sentence
"John Brown biography; main instigator of the Civil war"
"The GUD Magazine Issue 3 instigator is Debbie Moorhouse, who joined GUD as a copyeditor after her story Sundown was published in Issue 0."
"Bush may have never stated directly that Iraq was the main instigator of 9/11, but he repeatedly juxtaposed comments about 9/11 and Iraq in such a way that millions of Americans came to believe that Iraq was the main force behind the 9/11 tragedy."