Bolg was son and successor of the Moria Orc-chieftain, Azog. Azog killed Thorin’s grandfather, Thror, in Moria and was himself killed there by Thorin’s cousin, Dain. When the Great Goblin of the northern Misty Mountains was killed by Gandalf, Bolg secretly gathered an army of Wargs, Bats, and Goblins (including Wolf-riders). Travelling east from Mount Gundabad through the Grey Mountains, they attacked Erebor from the north and launched the Battle of Five Armies.
In that conflict between Goblins, Wargs, Men, Elves, and Dwarves, Bolg was constantly surrounded by bodyguards: Goblins of huge size with steel scimitars. When the battle drew down into the valley by Dale, Thorin Oakenshield and his small company charged from Erebor, pressing through the Goblin ranks before being encircled by the enemy. Bolg’s bodyguard struck down Thorin and killed his nephews as they defended his body, before the unexpected arrival of Beorn in an enraged, gigantic bear form. After carrying Thorin from the battle, Beorn returned, scattered the bodyguard, and crushed Bolg to death.
- “Dread has come upon you all! Alas! it has come more swiftly than I guessed. The Goblins are upon you! Bolg of the North is coming.” (by Gandalf with thunderous voice just before the Battle of Five Armies starts)