I have to admit that I nicked mine, from Monstrous Regiment, a Discworld novel by Sir Terry Pratchett. There was a vampire character in there called Maladict, and at the time I was looking for a cool name for a vampire in another RP I was taking part in. I hadn't been able to come up with any ideas of my own, so used that one instead. It was meant to be just for that game but it sort of stuck, and I've used it ever since.
I do feel bad about it, sometimes.