What is an aggressor?
An aggressor is a player who commits an act against another person. However, you do not become an aggressor globally, but rather you become an aggressor to the person against whom you committed the act. So the victim of your act sees you as an aggressor.

How do I become an aggressor?
Attacking another player, who is not an aggressor to you, will mark you as an aggressor to that person. This includes attacking another player with a spell, a summoned creature, a pet, or a wand. You will also be marked as an aggressor should you:

How long will I be an aggressor from the moment I become one?
You will be an aggressor for approximately two minutes real time.

Is there anything that would cause me to remain an aggressor longer than this?
Yes. By receiving damage or doing damage to another player, you will start over from the beginning and have approximately two more minutes.

If I am an aggressor, am I automatically labeled a criminal?
No. However, attacking an innocent will mark you as a criminal. See the criminal section for more details.

How will I know an aggressor when I see one?
They and their name will be GREY when your mouse pointer is over them.