Aggro

Whenever you deal damage to a monster, you generate aggro. Monsters attack whoever has the most aggro. Monsters can sometimes change target randomly.

Skills
Frontline gives you lots of aggro each second. If your level in Frontline is sufficient, the effects of random aggro can be reduced.

Sanctuary is like a reverse Frontline. It gives aggro to everyone in your party except you.

Lyrics is a passive skill that makes your damage generate less aggro.