Thrór was King of Durin's Folk and King under the Mountain, the grandfather of Thorin Oakenshield. In 2590 he led his people back from the Grey Mountains to the Lonely Mountain, and under him Erebor grew rich and famous again, and the town of Dale beneath it prospered on its trade.1,2
That wealth drew Smaug. In 2770 the dragon came down on Erebor and the town of Dale, and Thrór and his son Thráin escaped by a secret door with only a few of their people. Thrór gave Thráin the last of the Seven Rings of the Dwarves, and with one old companion, Nár, he wandered until in his age he resolved to look again on Moria.1,2
In 2790 he walked alone through the East-gate. The Orc Azog killed him and branded his own name on the severed head; Nár was told to take his fee and be gone. That outrage began the War of the Dwarves and Orcs, which ended nine years later at Azanulbizar.1,2
The map and key that Gandalf gave Thorin in The Hobbit, showing the secret door into the Mountain, were Thrór's. They passed to Thráin, who gave them to Gandalf in the dungeons of Dol Guldur before he died.3,1
Sources
Citations name the chapter rather than the page, so they work in any edition. The colour of each note shows what kind of source it is.
- Published story The Hobbit and The Lord of the Rings as Tolkien published them.
- Appendices Tolkien's own appendices to The Lord of the Rings.
- Appendices The Lord of the Rings, Appendix A, III, “Durin's Folk”
- Appendices The Lord of the Rings, Appendix B, “The Third Age”
- Published story The Hobbit, ch. 1, “An Unexpected Party”