Mudfolk are the original people, molded of clay by a god in primordial times. Both mud and Blood have a version of this creation myth, but according to the Blood, avatars of the twelve gods later came to earth and mated with mudfolk. Their offspring founded the clans of the Blood, who claim to be superior because of divine ancestry.

The mudfolk in Corymb are the indigenous inhabitants. Six generations ago, their lands were invaded by clans from Incus, who imposed their caste system and pantheon of gods on the conquered people. The mud have served the Blood ever since. They speak the Low, their original language, among themselves and the High to their masters.

Caste is considered immutable, an inborn trait. The offspring of matings between Blood and mud are always low caste. However, there are class differences within each caste that allow for limited mobility. There are mud people who have prospered through trade and Blood who are impoverished. The first must still defer to the second.