Óin (Son of Gróin)
From Tolkien Gateway
Son of Gróin, one of the Dwarves of the following of Thorin II Oakenshield who reclaimed Erebor from Smaug. He later travelled to Moria with Balin, and was lost in the ill-fated attempt to reoccupy Khazad-dûm, taken by the Watcher in the Water.