At the dawn of the world, many powerful spirits served the Enemy. Of these, perhaps the greatest were the Balrogs, great fire demons such as the one faced by Gandalf the Grey upon the Bridge of Khazad-dûm. Others of lesser strength were used by the Witch-king of Angmar to stir the bones of the dead lying beneath the mounds of the Barrow-downs.
Still another survivor of the Elder Days the Regmyl are lesser fire demons enthralled by the will of the Balrogs. While they are in fact minor spirits, they are among the mightiest of the sort: great brutes of evil will and fierce strength. Wherever a Balrog is or once was, it can be wagered that a Rogmul or two is not far away.
Romgul are found as powerful bosses in various higher-level dungeons: