Thorin fell victim to the sickness of greed. Dwarves are known for being greedy and proud, and when he realized the treasure of Erebor was his, including the Arkenstone, he became ill with Dragon Sickness. He began to value his wealth more than his friends, family, and own safety.
During the battle, Thorin was mortally wounded, but he made his peace with Bilbo before he died. When Thorin died, he was buried with the Arkenstone. Orcrist was laid upon his tomb. The blade would glow blue if Orcs should approach; thus, they could not take the Mountain by surprise.
The Dwarves were prone to this because of their love for treasures and mining. Bilbo was not affected because he is not greedy and wants to live a simple life under the comforts of home, he didn't also seek treasure. And he is more of a humble and resilient nature than the Dwarves.
Dragon-Sickness in Middle-earth | Tolkien Explained
Was Gimli immune to dragon sickness?
The philologist Susan Robbins writes in Žmogus ir žodis that with the words "I say to you, Gimli son of Glóin, that your hands shall flow with gold, yet over you gold shall have no dominion", Galadriel gives Gimli, alone of all the Dwarves, immunity to the dragon-sickness.
Indeed, "Thrór named it 'The King's Jewel'" according to Old Bilbo. In the books, this greed is partly caused by possessing one of the Seven Rings of Power, but in the films it is the Arkenstone itself that causes 'Dragon sickness'.
Although Smaug was the greatest of the Dragons of his day, he seems not to have been the last of his kind as Gandalf told Frodo Baggins that "there is not now any dragon left on earth in which the old fire is hot enough [to melt the Rings of Power]", indicating the presence of other, lesser dragons.
Why did Thorin go crazy? Thorin fell victim to the sickness of greed. Dwarves are known for being greedy and proud, and when he realized the treasure of Erebor was his, including the Arkenstone, he became ill with Dragon Sickness. He began to value his wealth more than his friends, family, and own safety.
Their deaths and Thorin's did not end Durin's line, although did end the branch which had Thror, Thrain, and Thorin Oakenshield. Thorin's cousin, Dain Ironfoot, became King after Thorin's death. Dain's son, Thorin Stonehelm, became King after Dain died in the Battle of Dale. The line continued on after that.
With Thorin's death in the battle, Dáin became King of Durin's Folk and King under the Mountain, the first not of the main line. After the battle, Dáin thanked the Great Eagles for their timely intervention, crowning their chief with gold and swearing the Dwarves to everlasting friendship with them.
After the death of Thorin in the Battle of Five Armies, Dain becomes King under the Mountain. He redeems the Arkenstone from Bard with a fourteenth of the treasure, which is used to re-establish Dale. Over the next three years, Bard rebuilds the city of Dale and becomes its ruler.
For a brief moment, Thorin distrusted Bilbo when they were captured by the trolls, but eventually saw that he was trying to This level of distrust even started when Thranduil turned his back on the dwarves, and also starting Thorin heavily disliking the elves.
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Thorin apologizes to Bilbo, saying that the world would be a better place if only more folks were like him. He asks for Bilbo's forgiveness. He bids farewell, and dies. Bilbo cries over the loss of Thorin – but is so glad that he made it in time to say goodbye and to make amends before he died.
Thror - King of Durin's Folk; gained dragon sickness after hoarding the gold his miners found. Thorin Oakenshield - Briefly had the dragon sickness and during it, he trusted no one, apart from Bilbo Baggins. However, after hearing the sounds of his friends and family echoing in his mind, Thorin was restored.
Smaug is aware of the return of Sauron, and was apparently intent on joining forces with him (although there was some amount of confusion as to whether the dragon's motives for an alliance with Sauron were).
It is later revealed that Smaug's attack on Erebor was all part of Sauron's design, meaning that Smaug and Sauron were in league with each other. Smaug was considered one of the highlights of the second film of the series; several critics hailed him as cinema's greatest dragon.
What happened to the Arkenstone after Thorin died?
As in the book, the Arkenstone is given by Bilbo (who, it is revealed, recovered it during his escape from Smaug) to Thranduil and Bard, in order to try to force Thorin to yield a share of the treasure. In the extended edition of the film, it was placed upon Thorin's chest following his death.
So when Tolkien began writing The Hobbit, and he first envisioned his character Smaug, he was paying homage to these great many mighty creations that had come before. The same is true of the dragon-sickness that features so heavily in the original The Hobbit novel.
Dwarves are the great craftsmen and miners of Middle Earth. By the nature of their profession, they look for gold and mithril, and ways to efficiently mine it from the earth. They have a natural talent for finding gold. For this reason, they have a reputation for greed among the other peoples.
