Grinnah is the chief interrogator of the Goblins of Goblin-Town, the Goblin that ensures that Thorin Oakenshield and company are brought before the Great Goblin.
Grinnah revels in every chance he gets to use his whip on the Dwarves. Although cunning and vicious, he is, like many Goblins, a coward at heart. Obsequious and fawning, in secret he loathes his master, the fat and capricious, Great Goblin.
He was first seen leading the captured Dwarves to his master, the Great Goblin, when he sees Orcrist he panics along with the other Goblins and starts attacking Thorin and company. He uses his whip on several of the Dwarves but was seemingly slain by Kíli when the Dwarf impaled Grinnah through the chest with his sword after Gandalf comes to the Dwarves aid.