In J. R. R. Tolkien's Middle-earth legendarium, Thorin Oakenshield was a Dwarf, the son of Thráin II and the grandson of King Thrór.

Born in the year 2746 of the Third Age (TA), Thorin was driven into exile by Smaug in 2770, along with the rest of the surviving Dwarves of the Lonely Mountain. At the Battle of Azanulbizar in 2799, when he was just fifty-three (a young age for a Dwarf) he marched with a mighty Dwarf-army into Nanduhirion beneath the East-gate of Moria. Thorin's shield was broken and he used a tree branch to defend himself, thus gaining the epithet "Oakenshield".

Thorin became King in Exile of Durin's folk when his father Thráin II died, as Thorin II Oakenshield.

In The Hobbit, he and twelve other Dwarves visited Bilbo Baggins on Gandalf's advice to hire him as a burglar, to steal back their treasure from the dragon Smaug. He especially wanted the Arkenstone, and was furious when Bilbo stole it to use as a bargaining counter with Thranduil, the Elvenking, who also laid claim to the treasure. The conflict was averted by an attack of Goblins and Wargs, and the Dwarves joined forces with the Elves, the Men of Lake Town and the great eagles to defeat them in what came to be called the Battle of Five Armies. During the battle Thorin was mortally wounded, but before he died he made his peace with Bilbo by commending the Hobbit's bravery and good character. His last words were, "If more of us valued food and cheer and song above hoarded gold, it would be a merrier world."

Thorin bore the Elven blade Orcrist into his final battles. He came upon it in a Troll stash (after barely escaping with his life from those very Trolls). He used it throughout the Quest of Erebor. It was buried with him after his death.