The dragon guarding the treasure beneath the Lonely Mountain in J.R.R. Tolkien’s The Hobbit is Smaug.
Smaug takes control of Erebor, the dwarf kingdom beneath the mountain, after attacking it and driving out King Thórin Oakenshield’s people. He then sleeps among the immense hoard of gold and jewels accumulated by the dwarves. Years later, Thorin leads a company to reclaim the mountain, with Bilbo Baggins serving as their burglar.
Bilbo discovers a weak, unprotected patch on Smaug’s underside and learns that the dragon’s armor-like scales are not completely secure. He also speaks with Smaug, whose pride and confidence make him reveal information. After Smaug attacks Lake-town, Bard kills him with a black arrow.
Smaug is not the largest dragon in Tolkien’s mythology; that distinction is generally associated with Ancalagon the Black. Glaurung belongs to the earlier First Age stories, especially The Children of Húrin, while Scatha is another dragon from Tolkien’s wider history.