Nith is a resident of the town of Ulthar where he works as a notary (a legal professional who witnesses the signing of documents). He was one of the town burgesses who helped pass the law that made it illegal to kill cats. (HPL: "The Cats of Ulthar")
The plain of Nith is also the name of a location within the blue-litten subterranean realm of K'n-yan. (HPL: The Mound)