How does Steinbeck present the character of Crooks in Of Mice and Men?

Although the men refer to Crooks with a derogatory term which was widely used at that time, Steinbeck treats the character sympathetically. When he is first described in chapter two, Candy, the old swamper, tells George and Lennie that he likes Crooks and tells them why he has a crooked back:

“Yeah. Nice fella too. Got a crooked back where a horse kicked him. The boss gives him hell when he’s mad. But the stable buck don’t give a damn about that. He reads a lot. Got books in his room.”

Crooks is segregated and sometimes the victim of racism, as with the episode in the bunkhouse at Christmas, involving "Smitty." Because of this, he is naturally "aloof" and suspicious. His segregation makes him understandably mistrustful as he angrily tells Lennie why he's not wanted in the bunkhouse:

“’Cause I’m black. They play cards in there, but I can’t play because I’m black. They say I stink. Well, I tell you, you all of you stink to me.” 

Crooks is also terribly lonely. He expresses this loneliness to Lennie in Chapter Four. He tells Lennie many of the details of his life, including how when he was a kid he played with white children. As an adult, however, he has grown bitter because he is generally excluded from companionship with the other men on the ranch:

“A guy goes nuts if he ain’t got nobody. Don’t make no difference who the guy is, long’s he’s with you. I tell ya,” he cried, “I tell ya a guy gets too lonely an’ he gets sick.”

When Candy enters the scene, talk turns to how George, Candy and Lennie are buying a farm. While Crooks is at first skeptical, he soon begins to believe in the dream and offers to go along and "lend a hand." Unfortunately, Curley's wife soon reminds Crooks of his position as a second class citizen, and at the end of the chapter he withdraws his offer go to with the men. 

Crooks is used by Steinbeck to help establish the theme of loneliness which pervades the novel. It's not a coincidence that the two loneliest characters in the book, Crooks and Curley's wife, also a second class citizen, would clash in Chapter Four as the girl threatens Crooks with hanging if he doesn't keep his "place." After this episode, Crooks is once again diminished as a black man in a world that views him with derision, and he retreats into the solitude of a lonely and distant figure:

Crooks had reduced himself to nothing. There was no personality, no ego—nothing to arouse either like or dislike. He said, “Yes, ma’am,” and his voice was toneless.