Noble Creatures are available only to those who donated at Wizard Lord level and above during the Kickstarter campaign.
If you backed at Wizard Lord, you could choose a selection of 12 of your creatures to be nobles - which means that they have more splendid weapons and attire, encrusted with gold. You would be able to select which creatures are to be ennobled, and you could change the selection before any battle.
For those of that backed at Wizard King level and above, all creatures were noble by default, but you could also select 12 of your creatures to have Royal Skins.
These are aesthetic changes, and have no effect on the creature's abilities. These skins were exclusive to backers - you can't earn them in game.