In J.R.R. Tolkien’s Middle-earth, the dragon who guards the treasure under the Lonely Mountain is Smaug.
Smaug appears in The Hobbit as the dragon who attacks the Dwarves’ kingdom of Erebor and takes possession of its immense hoard. He lives beneath the mountain until Bilbo Baggins enters his lair as part of Thorin Oakenshield’s company.
Bilbo discovers that Smaug has a vulnerable patch in his armor-like hide and later reports this weakness to Bard of Lake-town. Bard uses a black arrow to kill the dragon after Smaug attacks the town.
Smaug is distinct from Tolkien’s other dragons. Glaurung belongs to the mythology of the First Age, Ancalagon is a great dragon of the War of Wrath, and Scatha is associated with the Grey Mountains.