Thorin is born in Middle earth Prince Thrain, son of Thror. His brother Frerin was born in 2751 and their sister born in 2760. Around ten years later, Thorin was on the balcony and heard the winds picking up and looked up to see Smaug. He ordered Balin to sound the alarm and shouted below to his people that the Dragon had come. Smaug destroyed Dale and invaded the Mountain. Thorin was forced to flee the mountain, along with his kin. When he saw Thranduil, Thorin screamed to the elves for help, but their king refused to help, which led to his anger of Elves forever. The once proud race were forced to flee into exile and forced to find work wherever they could find it. Thorin never forgave, nor did he ever forget (The Hobbit: An Unexpected Journey").
During the war between Orcs of Moria and the Dwarves of Erebor, Thorin participated in such war. Thorin tries to run off and exact his revenge on Azog the Defiler. His father, Thrain, does not allow Thorin to go any further. This was the last time Thorin saw his father alive as Thrain disappears and never returns. He faced Azog the Defiler and earned the name, Oakenshield after using an oaken branch as a shield. During the battle, Thorin lost three of family members.
His grandfather was killed, Frerin died and his father went missing. After the , he searched body after body for his father, and found no sign of him (The Desolation of Smaug, An Unexpected Journey).
Sometime later, Thorin gains two nephews from his sister Dis and raises them as his own, often telling them tales of the Mountain .
Far into the east, far from the Blue Mountains, Thorin was searching for the places his father was last seen. He fallowed the rumor, but found no sign of Thráin was found. Thorin then settled in Bree at the inn of the Prancing Pony. He was nearly killed by assassins until Gandalf intervened and sat in front of him. This is how Thorin met Gandalf there in Bree, on the borders of the Shire.
Thorin in Bree around April TA 2940 after he met Gandalf the Grey in the inn of the Prancing Pony.
The King-in-Exile answers why he is there and is still confident that his father is still alive. Gandalf questions the ring Thrór wore and what became of it. Thorin answers that his grandfather gave it to his father before the battle of Moria, making Gandalf suspicious.
Since Gandalf was last seen with Thrain, Thorin asks what he asked. Thráin was then derived by Gandalf to rally the troops and reclaim Erebor. Thorin realized it was no chance meeting, and Gandalf admits it. He came across people who mistook him for a vagabond a price. Their problem is that someone placed a bounty on Thorin's head, to his scarce. Gandalf says its time for Thorin to take back his homeland and agrees to help take the Arkenstone. Thorin asks how they'll do it and Gandalf answers that they'll need a burglar (The Desolation of Smaug).
Thirteen was not a lucky number; Gandalf knew of Bilbo Baggins, a hobbit of the Shire, would willingly go along. Gandalf knew that his pride and quick temper would ruin t quest's reason to destroy Smaug. Knowing of Bilbo's low temper, He would be a calming influence. Thorin thought he was too soft to jOin because of the little use and because his mother died too early. But reluctantly let the Hobbit come along instead of preparing for war (Unfinished Tales).
At an unknown pOint, Thorin becomes very close with Bilbo, but an incident separates them. He makes it upon himself to find Bilbo again and reconcile with him.