Orlock is an unsual vampire, usually titled "Graf" (or "Count"). Unlike most such creatures, his appearance is barely human--bald, with bat-like ears, protruding fangs, claw-like fingers and an emaciated frame. His history is most famously chronicled in the silent motion picture Nosferatu. Other tales would seem to indicate he has been resurrected more than once from death.
Dennis Powers theorizes that Orlock is a kind of soul-clone of Dracula, created by alchemist Dr. Praetorius.
It may or may not be significant that Orlock resembles a Turok-han, a kind of primal vampire encountered by Buffy Summers (as well as an elder vampire she defeated known as The Master).