Who is Griphook from Harry Potter and the Deathly Hallows and what is their importance?

Griphook is a goblin. He once worked at Gringotts, and he is described as bloodthirsty. Griphook left his job because he was asked to do something that he considered beneath him, and he took his revenge by neglecting to tell anyone that the Sword of Gryffindor is fake. In the end, he helps Harry, Hermione, and Ron break into Gringotts right before running off with the Sword.