Hate

Hate, also called "aggro", is an invisible statistic tracked by mobiles. Entering mobile's threatened area, attacking with a weapon, or casting powers and abilities in the vicinity of mobiles will generate hate.

A mobile will always attempt to attack the player with the highest amount of hate, even if that player is flying or runs far from the spawn location.

Challenge

Barbarians, Crusaders, Sentinels, Templars, and Warriors receive a power called Challenge that immediately places them at the top of the targeted mobile's hate list. This enables those classes to fulfill their roles as "tanks" and absorb blows while other classes are free to deal damage uninterrupted.

Hate Reducer

Some weapon powers actually reduce your amount of hate, which enable those players to contribute to the tanking effort should they come under attack.

Amnesia

Necromancers, Priests, Warlocks, and Wizards receive special powers that completely wipe a monster's hate table.

Invisibility

Using Sneak, Hide, or any other invisibility spell to become invisible will remove a character from a mobile's hate table.