BalrogBalrog - "It came to pass that in the middle of the Third Age Durin was again its king, being the sixth of that name.  The power of Sauron, servant of Morgoth, was then again growing in the world, though the Shadow in the Forest that looked towards Moria was  not yet known for what it was.  All evil things were stirring.  The Dwarves delved deep at that time, seeking beneath Barazinbar for mithril, the metal beyond price that was becoming yearly ever harder to win.  Thus they roused from sleep a thing of terror that, flying from Thangorodrim, had lain hidden at the foundations of the earth since the coming of the Host of the West: a Balrog of Morgoth.  Durin was slain by it, and the year after Náin I, his son; and then the glory of Moria passed, and its people were destroyed or fled far away." ~The Return of the King (Appendix A)