The Dragon Slayers
In human lands, the concept of vassalage governs the politics of the land. In theory, every noble is a someone’s vassal (except for the King), granted lands and protection by their superior in exchange for fealty.
The strictest definition of “nobility” is of someone who has been granted vassalage in this way, but established noble families have a tendency to sneer on anyone who holds lands or titles without serious geneological backing (or force of arms). In practice claiming to be of “noble blood” without at least two or three generations of distance between you and “common blood” is a serious faux pas and is a quick ticket to being excluded from high society. Nobles prefer the nouvaux riche to be aware of their place and not get ideas above their station, no matter how much money they have or how many swords they have to call upon.
Legally, no-one can own lands claimed by the King without being granted them through the chain of vassalage. For this reason those who own fiefs or other landholdings often get extremely rich off the back of them – they technically own the land that the common people work, and so therefore can exact rent and other taxes. On the outskirts of the Kingdom, however, it is more difficult to assert ownership and for practical purposes anyone who can control an area of land effectively owns it.
In the early days of his rule the King would frequently grant areas of land to those on the borders who had taken it from the wilderness, other humans who resisted the King’s offer of unity, or the other races and a number of noble families are descended from these frontier-expanding pioneers.