Óin was the son of Glóin, and succeeded his father as King of Durin's folk, reigning from 2385 to 2488 Third Age. He lived with his kindred in the Ered Mithrin, and saw the takeover of Moria by Orcs, which had multiplied by then as a result of Sauron's growing presence in the Mirkwood.
A much later Óin accompanied Thorin Oakenshield on his quest in The Hobbit. He was the son of Gróin, the grandson of Borin, the younger son of King Náin II, and so could claim direct descent from Durin the Deathless himself. Glóin, another of Thorin's companions, was his brother. Óin was later lost when he journeyed with Balin to reclaim Moria.
