Which Tolkien novel features the dragon Smaug as its central antagonist?

The Tolkien novel featuring the dragon Smaug as its central antagonist is The Hobbit.

Smaug occupies the Lonely Mountain, also called Erebor, after driving the Dwarves of the kingdom of Erebor from their home. He guards their immense treasure, including the Arkenstone, for many years. Thorin Oakenshield leads the company seeking to reclaim the mountain, and Bilbo Baggins accompanies them as their burglar.

Bilbo’s conversation with Smaug is one of the book’s best-known scenes. By learning about the dragon’s weak point and sharing information indirectly, Bilbo helps expose a vulnerable place in Smaug’s armour. The dragon later flies to attack Lake-town, where Bard kills him with the Black Arrow.

Smaug does not appear as a principal character in The Lord of the Rings. The later trilogy refers to the consequences of his death and to the Battle of Five Armies, but the dragon’s main story belongs to The Hobbit.