In the Fall of Arnor, Grabûnhold was said to be the Brother of Ardorlan (Prince of Cardolan). When some armies of Cardolan escaped to Fornost for the Battle of Fornost, he came with the surviving Cardolan armies.
In the Battle of Fornost, He Defended the Citadel along with Eärnur & the King of Fornost. Some of Angmar's armies tried to break through the walls by damaging them, But didn't break through so the armies destroyed the Front entrance to Fornost. By the time, the Main Gate to Fornost's citadel was broken through as he charged to the armies of Angmar. The Witch-King managed to kill Grabûnhold by blasting back some armies. Grabûnhold died on the stairs of Fornost's Citadel.
When Fornost's Citadel was left in ruins for four days, Some of Angmar's forces grabbed some corpses of Fornost's Soldiers. Morgomir founded Grabûnhold's corpse and used the Socerers to corrupt his soul. His soul was corrupted & he transformed into a Wight. When the forces of the Witch-King returned to Angmar, he became the King of the Wights. The Witch-King then gave Grabûnhold, the Royal Barrow where Captain Carthaen died. Inside is a tunnel to a underground cave where Barrow Wights lived for a long time.