

Thorin intended to infiltrate the Lonely Mountain and retake the treasure from Smaug. Thorin then took a contingent of twelve Dwarves to visit Bilbo Baggins in order to hire him as a burglar for their mission. He gave Thorin a map and key that he had received from Thráin in Dol Guldur before he died. In TA 2941, Gandalf the Grey found Thorin in The Prancing Pony at Bree and set in motion a scheme to retake the mountain. Thorin became King-in-Exile of Durin's Folk in TA 2850 after his father went missing, and died in the dungeons of Dol Guldur. At some point in the fighting, his shield broke, and using an oaken tree branch found on the ground as a shield, he gained the epithet "Oakenshield," which would remain with him even in death. He fought with one of the Dwarven armies beneath the East-gate of Moria.

This was demonstrated when he participated in the Battle of Azanulbizar in TA 2799. While in exile, he quickly grew to become a capable warrior. Early in his youth, he and the other Dwarves of the Lonely Mountain were forced to flee by the dragon Smaug in TA 2770. Thorin II was born in TA 2746 to Dwarf prince Thráin II in the city of the Lonely Mountain.
