"… they grew immensely rich and famous, and [Thrór] was King under the Mountain again, and treated with great reverence by the mortal men who lived to the South, and were gradually spreading up the Running River as far as the valley overshadowed by the Mountain."
—Thorin relating the outcome of his grandfather's return to Erebor
He returned to the Lonely Mountain following the death of his father Dáin I in TA 2589, he rediscovered the Arkenstone and refounded the Kingdom. In TA 2770 with the coming of Smaug, King Thrór was forced into exile until he was later murdered by Azog in TA 2790.
The son of Thráin II he succeeded his father in TA 2850 as de jure king. Thorin II Oakenshield was briefly restored to the throne in TA 2941 after the death of Smaug. He was killed shortly afterward in the Battle of the Five Armies along with his nephews Fíli and Kíli.