Gróin was born in TA 2671. He was of the and was likely born in the Lonely Mountain (Erebor). Gróin had an older brother named Fundin, who was the father of Balin and Dwalin. Gróin had two sons: Óin, born in TA 2774, and Glóin, born in TA 2783. Both of Gróin's sons undertook the quest of the Lonely Mountain, and Glóin was the father of Gimli of the Fellowship of the Ring. Gróin died in TA 2923. For all his genealogical importance, nothing more is known of his life. His dates of birth and death, though, state that he was alive at the time of Smaug's Sack of Erebor, and the War of the Dwarves and Orcs twenty-nine years later. It is likely that he was present at both these events.