Dwarves of the Lonely Mountain

The original home of the Longbeards, the Dwarves of Durin's Folk, had been the majestic mountain-city of Khazad-dûm. After dwelling there for many millennia, they were driven out by a Balrog, and scattered into the Wild as their ancient mansions fell into darkness. Their King, Náin I, had been slain by the Balrog, but his son Thráin I led many of the Longbeards away to the northeast. There he founded a new Dwarf-kingdom beneath the Lonely Mountain, Erebor above the Long Lake.

The followers of Thráin I were the founding Dwarves of the Lonely Mountain, but that first kingdom did not last long. Thráin's son Thorin I saw that most of his people were settling in the Grey Mountains, to the north and west of Erebor, and he moved the King's seat to be with his people there. It is unclear whether the Lonely Mountain was completely abandoned at this time - it seems likely that at least some Dwarves remained - but the royal house was resettled in the far north, and remained there for five generations.

After King Dáin I was slain by a Dragon, his heir Thrór determined to lead the Longbeards back to Erebor, and refound the Kingdom under the Mountain. In his time the Dwarves of the Lonely Mountain reached the height of their wealth and fame. News of that wealth reached ears of the Dragon Smaug, who descended on the Lonely Mountain and claimed it for himself: yet again the Longbeards were driven out of their home into the wilderness.

Eventually the wandering Dwarves settled far to the west, in Ered Luin, where they plotted vengeance on the Dragon Smaug. It was Thrór's grandson Thorin who finally achieved this, with the help of the Wizard Gandalf and Bilbo Baggins. Thorin himself did not survive long enough to rebuild his grandfather's kingdom: he was slain in the Battle of Five Armies. His cousin Dáin Ironfoot, who had led the Dwarves of the Iron Hills, became the new lord of the Lonely Mountain, and ruled there as King Dáin II until the time of the War of the Ring. Dáin was slain in that war, but the Kingdom under the Mountain survived, and the Dwarves still dwelt there as the Fourth Age dawned.