The name Crebain comes from The Lord Of The Rings, they are the crow-like creatures used by the evil forces as scouts while the heroes walk through Hollin. They are the ears and eyes of the enemy. Crebain is the plural form of craban.
The stage name 'Ancalagon the Black' also comes from LotR. According to Tolkien, Ancalagon the Black was one of the mightiest dragons ever to have lived in Middle Earth.