Smaug is the dragon faced by Bilbo Baggins in J.R.R. Tolkien's The Hobbit.
Smaug occupies the Lonely Mountain and has taken the treasure of the dwarf kingdom of Erebor. Thorin Oakenshield leads a company to reclaim the mountain, and Gandalf recruits Bilbo as their burglar. Bilbo enters the mountain, speaks with Smaug, and learns about a vulnerable patch in the dragon's armored underside.
The information reaches Bard of Dale through the thrush that overhears Bilbo's conversation. Bard then uses the Black Arrow to kill Smaug during the dragon's attack on Lake-town. Smaug's death changes the balance of power and helps trigger the Battle of the Five Armies.
Smaug is not the dragon from Tolkien's earlier legend of Túrin, Glaurung, nor is he Ancalagon, the great dragon of the First Age. Those creatures belong to different parts of Tolkien's mythology. Smaug is especially notable for his fluent, manipulative speech and his obsession with treasure.