In J.R.R. Tolkien’s The Hobbit, the dragon guarding Erebor is Smaug.
Smaug is a powerful, intelligent dragon who attacks the Dwarf kingdom beneath the Lonely Mountain and drives its inhabitants into exile. He then occupies the mountain and hoards its treasure for many years. His presence is the central threat that motivates Thorin Oakenshield and the company of Dwarves to reclaim Erebor.
Smaug is especially notable for his conversation with Bilbo Baggins, who enters the mountain while the dragon sleeps. Bilbo discovers a bare patch in Smaug’s otherwise armored underside, and a thrush later tells Bard about this weakness. Bard uses the information to kill Smaug with the Black Arrow.
Readers sometimes confuse Smaug with Tolkien’s other dragons. Glaurung appears in The Silmarillion and The Children of Húrin, while Ancalagon the Black belongs to the First Age. Smaug is the dragon specifically associated with The Hobbit, Erebor, and Lake-town.