The Balrogs, sometimes called Balrogath, were menacing creatures about twice the height of a man consisting of fire and shadow. Created by Morgoth, Balrogs induced great terror in all and were among Morgoth's most feared minions during the First Age.
During the First Age, Balrogs were among the most feared of Morgoth's forces. When his Fortress of Utumno was destroyed by the Valar, seven fled and lurked in the pits of Angband. The Balrogs were first encountered by the Elves during the Dagor-nuin-Giliath (Battle-under-Stars) in the First Age. After the great victory of the Ñoldor over Morgoth's orcs, Fëanor pressed on towards Angband, but the Balrogs came against him. He was mortally wounded by Kosomot, Lord of Balrogs. Though his sons fought off the demons with an army of elves at their side, Fëanor died of his wounds soon after, and his spirit departed and moved on peacefully to afterlife. Another major encounter was in the Battle of Unnumbered Tears. Gothmog, High Captain of Angband, led the invasion. He threw aside Hurin and Turgon, turned upon Fingon and killed him with the help of another Balrog, winning the battle for Morgoth's forces. During the Fall of Gondolin, Ecthelion managed to kill Gothmog at the cost of his own life. Another Balrog is confronted when he attacks Tuor and those attempting to escape the siege. Glorfindel fought the Balrog to give his friends a chance to escape.
The battle ended with Glorfindel casting down the Balrog from the mountain but being pulled down along with the demon. The last Balrogs fought in the War of Wrath, but were either slain or forced to retreat. Most of the Balrogs of Morgoth were destroyed during the War of Wrath at the end of the First Age, but some few "fled and hid themselves in caverns inaccessible at the roots of the earth.
During the Third Age, it was discovered that one of these had hidden deep beneath the Misty Mountains, near Moria. That was Malraugin, also known as "Durin's Bane", the best-documented of the Balrogs. The Dwarves of Khazad-dûm had accidentally awakened him while they were mining too deep for Mithril. Malraugin drove the dwarves from their homeland in Moria. Later, in his confrontation with the wizard Gandalf and the the Fellowship of the Ring, he pursued them to the bridge of Khazad-dûm. Gandalf fought the Balrog allowing the Fellowship to escape Moria.