Durin's Bane

"The Dwarves delved too greedily, and too deeply. You know what they awoke in those mines; shadow. Flame."

-Saruman alludes to Durin's Bane

This particular Balrog, who's name was unknown, and was referred to as Durin's Bane, or the Nameless Terror, is a Balrog encountered in the first volume of Tolkein's Lord of the Rings trilogy, and was probably the last of it's kind. It was accidentally awakened by the Dwarves in Moria, who delved too deeply into the mines in their insatiable appetite for more precious Mythrill. Upon awakening, the Balrog killed or drove out the Dwarves with all speed.

In TA 3019, the Fellowship of the Ring are forced to enter Moria. The Balrog discovers them, scares off the goblins surrounding the Fellowship, and follows them to the bridge of Khaz-a-dum. The Fellowship of the Ring make it across the bridge, but Gandalf stays behind, and prevents the beast from crossing, shattering the Balrog's sword. He uses his magic staff to break the bridge, but as Durin's Bane falls into the chasm below, it wraps its fiery whip around Gandalf's legs, and drags him down with it.

After a long fall, Gandalf and the Balrog crash into a huge underground lake, which extinguishes the flames of the Balrog's body, leaving it severely weakened and forcing it to retreat from the wizard. Gandalf then pursues the beast for several days, chasing it out of the tunnels and onto the highest peak of the mountains of Charadras, where its flames explode back to life. The Balrog is eventually defeated and cast down onto the mountain side, dead. However, this is only the Balrog's physical body, so its spirit's fate is unknown.