Balrog

Good old Tolkien's own brand of demons, the Valaraukar or, after some linguistic drift, the Balrogs, were demonic servants of Middle Earth's original BBEG Morgoth/Melkor.

The descriptions of the critters are a bit vague, to the point fans have spent quite some energy arguing whether they actually have wings or not. Still, what they boil down to are a demonic being if shadow and fire, wih whips of flame.

As one of the mightiest foes the Fellpwship of the rings faces, and certainly of awesome appearance, the fiery and shadowy demon is copied by many of the later fantasy universes that were inspired by LOTR. Of course, how much originality one can attribute to the concept of a fire+demon creatuee, in a Christianity influenced Europe, is a question for another debate.

DnD filed off the serials by renaming the local expy to Balor, leading to some potential for confusion, or, as the original article reads:

"THERE IS NO SUCH THING AS A BALROG IN DUNGEONS AND DRAGONS. The balor / Type VI is totally different."

But then, who would mind, really? flaming whips are awesome either way...