Yet so great was the power of Morgoths uprising that in ages forgotten he contended with Manwe and all the Valar, and through long years in Arda held dominion over most of the lands of the Earth. But he was not alone. For of the Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into his darkness; and others he corrupted afterwards to his service with lies and treacherous gifts. Dreadful among these spirits were the VALARAUKAR, the scourges of fire that in Middle-earth were called the Balrogs, demons of terror.


John Ronald Reuel Tolkien
Simarillion, Valaquenta 35