What are Balrogs?
From: Erik Tracy
Balrogs are Maiar, or primeval spirits, that Morgoth, the Dark Lord of the First Age of Middle-earth, seduced to his service. They assumed a physical form while in Middle-earth that was powerful and dreadful to behold. The word Balrog means "Demon of Might" in Sindarin; the Quenyan form is Valarauko. The following quotes are from the Silmarillion:
"For of the Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into the darkness; and others he corrupted afterwards to his service with lies and treacherous gifts. Dreadful among these spirits were the Valarauko, the scourges of fire that in Middle-earth were called the Balrogs, demons of terror."
"And in Utumno he gathered his demons about him, those spirits who first adhered to him in the days of his splendour, and became most like him in his corruption: their hearts were of fire, but they were cloaked in darkness, and terror went before them; they had whips of flame. Balrogs they were named in Middle-earth in later days."
Fear of the Middle-earth, deamons of fire, servants of Melkor... Find out all about Balrogs on this page.