Why is crooks a part of the book ';of mice and men'; ?

english homework!Why is crooks a part of the book ';of mice and men'; ?
He's isolated from the rest of the men and pretty much stays to himself in his room when he isn't working. First Lennie and then Candy goes into Crooks' room, and Crooks, for just a little while, forgets the racism that alienates him and talks to Lennie and Candy as men. When Curley's wife comes in, all of this ends. The men try to get her to leave, and she gets angry and plays the racism card at Crooks when he stands up to her. She puts Crooks back in his place as the only black man on the ranch who isn't allowed to even socialize with the whites. Her cruelty reminds Crooks of his situation and that he can't do anything about it. This is why Crooks tells Candy he really didn't want to go work with them on their farm.