A very simple class.
The Nobles are very much like the class of Captain, Commanders and other Warlords. Their specalities lies within useful Auras, of which compliment their allies the best.
The class of the Noble is although very different from other classes since you can not choose to become one, you are either born as one, or not.
Note: only Royals can be born as Nobles, and this is why it is such a rare class.
Most races have at least a few Nobles within their Keep, Citadel or Tree (and so on). but a few races do not have nobles. These are either beasts, orcs, ogres, some humanoids, and summons. (to name a few)
Nobles can also Multiclass into a few other classes such as Warrior, or a Wizard of some kind.
Some classes are impossible for them to fuse with, though, like the Rogue class and Berserker. It's just not in their nature to either steal or go on a mad rampage of blood.
Arthas, the present Lich King, was once a Noble and Multiclassed into the holy arts of the Paladdins.
P.S. there might be royals within the orc and ogre races but they are not Nobles. You also need at least a few good manners and the ability to speak a flawless english before you can be classified as a Noble.