Noble
The nobles were a race of humans on Scadrial.
The nobles were effectively created by the Lord Ruler when he forcibly divided the people of the world. The nobles were descendants of the people who supported the Lord Ruler on his rise to power. When Rashek took up the power at the Well of Ascension, he used it to alter mankind as a whole to be more capable of dealing with ash, but he also made physiological changes between the different groups of people; noblemen and skaa. The nobles were made taller, stronger, less fertile, and more intelligent. These physical differences were small, and have mostly been erased by noble and skaa interbreeding over the thousand years of the Final Empire's history. All Allomancers had a noble descendant somewhere along their heritage. This is because when the Lord Ruler came to power, he gave his initial supporters beads of lerasium which imparted to them the powers of a Mistborn.
Culture
The life of the nobles was rife with secrecy and plotting. Almost all nobles were driven by gaining money, power, or social prestige.
All nobles were divided among different Houses. Each house had its own agenda and worked towards its own betterment. Each house individually had its own political enemies and allies. Generally, leadership of a house was inherited.
Powers
Many (but not all) nobles were Allomancers to some degree. Very few, however, are actual Mistborn. This was due to the thinning of Preservation's power through the generations of nobles.