The elder son of Groin, Oin lived for over 200 years in the Third Age, A member of Thorin and Company, he remained in Erebor after Smaug's death in T.A. 294. In T.A. 2989, he accompanied Balin to Khazad-dum. Five years later, Oin was slain by a tentacled Watcher in the Water at the Orc-infested stronghold also known as Moria.