The Blood are a hidden race of exceptional beings living on Earth, undetected by humanity as a whole. There are a number of secret societies formed either by the Blood, or by humans to watch them.

The Blood can and do interbreed with humans. The offspring of such a union may or may not manifest any Blood abilities - there are many humans with recessive Blood genes from a distant ancestor. Accordingly, every so often a child will be born to two apparently normal human parents, only to manifest Blood traits later in life.

Most of the origin myths of the Blood include an explanation for their parentage - research done by the various factions indicates that all of the Blood have a small number of common ancestors. The number of Blood progenitors differs depending on who you ask, but the range is generally accepted to be no more than twelve, and as few as one.