J.R.R. Tolkien> The Lord of the Rings / The Silmarillion
The Ring of Thrór was the first of the seven Dwarf-rings to be given to the dwarves by the Elves of Eregion and the last one to be recovered by Sauron. It belonged to the dwarves of Durin's line and the first to hold it was Durin III. It remained in this line for thousands of years until the reign of Thrór at Erebor. During his reign, Smaug drove the dwarves out of their kingdom and almost all the treasures of the house were lost. The ring escaped this plundering and Thrór passed it on to his son Thráin (the father of Thorin), who later set out on a quest to reclaim his home. During this quest, he was captured and slain by the spies of Sauron and the ring was lost.