Grór was born in Grey Mountains (Ered Mithrin) as the youngest of three sons born to Dáin I. His older brothers were Thrór and Frór. After the death of his father in TA 2589, he and his brother left the Grey Mountains and while Thrór went back to the Lonely Mountain (Erebor), Grór went further into the east and in TA 2590 he established the Kingdom of the Dwarves in the Iron Hills. Two hundred years later, just before the Battle of Azanulbizar (or Nanduhirion) in TA 2799, he thought himself too old to go, and instead sent his son Náin and grandson Dáin II, the king of the dwarves at the Iron Hills at the time of The Hobbit. Grór was indeed old, for he died not too long after in TA 2805.