Smaug is the dragon who lives beneath the Lonely Mountain in The Hobbit.
Smaug seized the Lonely Mountain and its treasure from the Dwarves of Erebor before the main events of the novel. His attack drove King Thrór’s people into exile and left the surrounding town of Dale destroyed.
Bilbo Baggins enters the mountain with Thorin Oakenshield’s company and speaks with Smaug while trying to discover the dragon’s weakness. Smaug’s conversation with Bilbo is one of the book’s most famous scenes because it combines riddling language, suspicion, and psychological manipulation.
Smaug is sometimes confused with Tolkien’s other dragons, including Glaurung and Ancalagon from the First Age stories. Those dragons belong to earlier periods of Middle-earth’s history. Smaug belongs to the later Third Age and is defeated after leaving the mountain to attack Lake-town.