King under the Mountain

The King under the Mountain also called the King of Erebor is the title of the Dwarven ruler who resides at the Lonely Mountain of Erebor. The King under the Mountain was also by right the King of Durin's Folk.

In The Hobbit, the dragon Smaug was held to be the only "king" of Erebor. Thorin Oakenshield was in fact in line to be the only rightful King under the Mountain.