IPA: /ˈɪn.stɪ.ɡeɪ.tər/
KK: /ˈɪnstɪˌɡeɪtər/
A person who causes or encourages something to happen, often in a negative way, like starting trouble or conflict.
The instigator of the protest was arrested for inciting violence.
Instigator → It is formed from "instigare" (meaning to incite or urge on) and the suffix "-or" (meaning one who). The word "instigator" refers to one who incites or urges others to take action, often in a provocative manner.
Think of someone who 'urges on' ('instigare') others to act — that's why an instigator is someone who incites action.