Champion
From Townstons
Champion mobs are more powerful and are more rarely seen than normal mobs. They can appear within a group of mobs and have auras surrounding them. If you mouse-over a Champion it will say (Champion) at the bottom-right of the screen, under its name, and usually give its bonus percentages in Monster Health, Damage, and Loot. Most Champions have unique names. They are less powerful than Heroes.
A list of the unique champions.