instigant
/ˈɪnstɪɡənt/
noun
- A person who provokes or stirs up an action, event, or conflict, often in a negative way.
- Historians identified the general as the main instigant of the rebellion.
- The coach warned the players not to listen to the instigant who was trying to start a fight.
- The protest was peaceful until an instigant began shouting insults at the police.
Antonyms