Thrall

A human who has been magically bound into a servitude to a supernatural being, most often vampire, demon, or youkai. The binding might require exchange of bodily fluids, like blood or semen, or it might not. In return for their submission, the human usually receives longevity and a portion of their master's powers.

Differs from Familiar, which are spirits bound to the service of a magician or a supernatural entity, while Thralls are usually humans (or members of another mortal species).