Balrog

Balrogs were Maiar spirits that were lured my Morgoth (The First Dark Lord) and took a demon-like shape as a result.

One of the most famous/fashionable Balrogs has to be Durin's bane living in Moria. Durin's Bane was one of the badasses that existed before the creation of the world (similar to Gandalf and Saruman). He was called Durin's Bane because he kicked the hypothetical shit out of a dwarven king called Durin II.