- You may be looking for the demon of the same name.
The Beast was the name given to a species of flying extra-dimensional parasites. They were normally invisible to most species. They would travel from planet to planet, feeding on the life force of the native populations without harming them, and departing after having their fill.
The Beast travelled to Benelisa and fed on the natives, but since their population was so small, the Benelisans were unintentionally wiped out. Before dying, they sent out Azoth to locate and destroy the Beast. (PROSE: The Taint)