The dragon who hoards treasure in J.R.R. Tolkien’s The Hobbit is Smaug.
Smaug occupies the Lonely Mountain, also known as Erebor, after driving out the Dwarf king Thrór and his people. The treasure beneath the mountain includes the Arkenstone, a treasured heirloom of the Dwarves. Thorin Oakenshield’s company sets out to reclaim the kingdom, with Bilbo Baggins serving as the burglar.
Bilbo discovers a weakness in Smaug’s armor and later reveals it to Bard of Lake-town. Bard uses this information to strike the dragon’s unprotected spot with the Black Arrow. Smaug’s death changes the political balance of the region and leads to the Battle of the Five Armies.
Tolkien created other dragons, including Glaurung and Ancalagon, but they belong chiefly to the earlier mythology of The Silmarillion. Smaug is the dragon specifically associated with The Hobbit.