An aggressor is someone who attacks first or starts a conflict without being provoked. When two countries go to war, the aggressor is the one that invaded or attacked without justification. When a fight breaks out on the playground, the aggressor is the person who threw the first punch or started pushing, not the person who defended themselves.

An aggressor doesn't wait to be threatened: they make the first hostile move. In sports, an aggressive player might play hard and take risks (which is usually fine), but an aggressor crosses the line into starting actual fights or deliberately trying to hurt opponents.

Understanding who the aggressor is matters because it helps determine who's responsible for a conflict. If someone shoves you and you push back to protect yourself, you're not the aggressor, they are. Teachers, referees, and judges often need to figure out who started the trouble to decide consequences fairly.

Being assertive or competitive is different from being an aggressor. Assertive people stand up for themselves and go after what they want, but aggressors initiate conflict and attack others. The key difference is that an aggressor makes the first move to harm or dominate someone else.