‘What is the importance of Crook’s in the novel?’

Well, for one thing he is black. That means he doesn't live with the rest. He is always the outsider because of his color and keenly aware of this. He even accepts Curly's wife dismissal of him as being inferior. Steinbeck uses Crooks to portray the very commonplace racism of the time. What is important to me is that even as a black man, inferior as he accepts himself to be, he is cruel to Lenny and toys with him. That places Lenny even lower on the social scale.