one is a physical creature and the other is like a ghost, but immortal and it does what it wants, which is make mischief and cause chaos.
if anyone follows the Interview with The Vampire book series, the two original vampires Akasha and Enkil were possesed by this demonic spirit named Amel.
Amel was a powerful spirit first mentioned in the novel
The Vampire Lestat. He was the essence of
vampirism, being the source of their powers as well as their bloodlust, residing in the
Sacred Core. Fusing with
Akasha, then consumed by
Mekare, then
Lestat. Later having a body created for him, and separating from Lestat and all Vampires becoming a
Replimoid once again.