The fictional dragon who guards the treasure in J.R.R. Tolkien’s The Hobbit is Smaug.
Smaug occupies the Lonely Mountain, also called Erebor, after driving out the Dwarves of Durin’s folk. He sleeps on their accumulated treasure and becomes the central threat of Bilbo Baggins’s journey with Thorin Oakenshield and the company of Dwarves.
Smaug is notable not only for his size and destructive power but also for his intelligence, speech, and skill at questioning others. Bilbo first encounters him while carrying out reconnaissance inside the mountain. During their conversation, Bilbo uses riddling names rather than immediately revealing his identity.
A concealed weakness in Smaug’s armor-like underside allows Bard the Bowman to kill him with the Black Arrow. Smaug is sometimes confused with Tolkien’s other dragons, including Glaurung and Ancalagon, but those characters belong to earlier legendary histories rather than The Hobbit.