Balrog vs 200 000 dwarves ?

[Inziladun]

Originally Posted by Boromir88

It's possible he had a particularly fell and powerful spirit, like Sauron who housed evil spirits into wolf bodies. Yet, "fell spirit" doesn't mean maiar.

Glaurung seems to have been a body containing some measure of Morgoth's own spiritual essence.

And there right before [Nienor] was the great head of Glaurung who had even then crept up from the other side; and before she was aware her eyes looked in his eyes, and they were terrible, being filled with the fell spirit of Morgoth, his master.

UT Narn I Hîn Húrin

I think Glaurung himself, as the "father" of dragons, was primarily an extension of Morgoth's will. Later dragons that were bred (by unknown means) were, I think, more independent.

x/d with Cellurdur