One who is in the process of application to become a In a word, vampires. There are two branches of Night-Children, but both stem from Notte, as he was the first. More in Notte’s family. Only humans can be turned into vampires, and the human has to pass a series of tests and take a number of classes both before and after turning.
He’s one of the oldest living beings among the Mythos. The father of all vampires (or Night-Children, as they’re called),... More is pretty darned picky about who’s allowed to be turned.
As an aside, A vampire, and Notte’s oldest surviving child (not his first, however). More takes whomever she darned well pleases, but she has to keep them under the radar.