Who is Thorin Oakenshield's grandfather?

Thorin Oakenshield’s grandfather is Thrór.

Thrór was a Dwarf king and the grandfather of Thorin II. He ruled the Kingdom under the Mountain at Erebor before Smaug attacked, drove the Dwarves into exile, and seized their hoard. Thorin’s quest in The Hobbit is therefore rooted in the loss of his grandfather’s kingdom and the restoration of his family’s royal line.

Thorin’s father was Thráin II, who survived the fall of Erebor but later disappeared after suffering imprisonment and torment at Dol Guldur. This makes the family sequence Thrór, Thráin II, then Thorin Oakenshield. The similar-looking names are easy to confuse, especially because Tolkien uses several related names beginning with “Thr-” and “Thrá-.”

Thrór’s later history is also tied to the Dwarves’ war against the Orcs. He was killed by Azog in Moria, an event that intensified the feud between the Dwarves and Orcs. Dáin Ironfoot, one of Thorin’s relatives, eventually succeeds Thorin after the Battle of Five Armies.