War of Wrath
This Balrog appears in "The Lord of the Rings", encountered by the Fellowship of the Ring in the Mines of Moria. It survived the defeat of Morgoth in the War of Wrath, escaping to hide beneath the Misty Mountains. For more than five millennia, the Balrog remained in its deep hiding place at the roots of Caradhras, one of the Mountains of Moria, until in the Third Age, the "mithril"-miners of the Dwarf-kingdom of Khazad-dûm disturbed it. The Balrog killed Durin VI, the Dwarf-King of Khazad-dûm, whereafter it was called Durin's Bane by the Dwarves. Avarice, principally for "mithril", drove the dwarves to go too deep and awaken the Balrog.