The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
He was granted Stewardship of the settlement by Thorin II Oakenshield before his departure to re-capture Lonely Mountain (Erebor), a quest in which Thorin would die. With Thorin's death, Gormr became the ruler of the settlement and his clan quickly overran the Durin's Folk residing in the region outside the city by the time of the War of the Ring. In order to bring King Skorgrim back to life, he corrupted Thorin's lands with magic by raising the dead. He was caught by Dwalin's group when they entered Skorgrim's tomb and was killed in the ensuing fight but Skorgrim was successfully resurrected. Dwalin would then take his place as Steward of Thorin's Halls and his Longbeards would recover the entire region from the Dourhands.