King under the Mountain

The term King under the Mountain was used in a good deal of Celtic mythology (and later fairy tales) to refer to the ruler of the supernatural creatures particular to a given location, particularly the sidhe.

---

In J. R. R. Tolkien's fantasy universe of Middle-earth, the King under the Mountain is the title of the Dwarf ruler who resides at the Lonely Mountain.

---

In The Hobbit, the dragon Smaug held this title. Thorin was in line to be the King under the Mountain.