Crooks is the black stable buck character in Steinbeck's Of Mice and Men. He takes care of the horses and mules and lives by himself in the barn. Because he is black, he's segregated from the other men on the ranch, who are all white. He is also the victim of racism. The theme of his loneliness revolves around not having another guy around to talk to as well as the prejudice he faces.
He is envious of George and Lennie because they travel around together and have each other as companions, sharing experiences and conversations. Crooks expresses this envy when he's talking to Lennie in his room in the barn in chapter four:
"I seen it over an’ over—a guy talkin' to another guy and it don’t make no difference if he don’t hear or understand. The thing is, they’re talkin’, or they’re settin’ still not talkin’. It don’t make no difference, no difference.” His excitement had increased until he pounded his knee with this hand. “George can tell you screwy things, and it don’t matter. It’s just the talking. It’s just bein’ with another guy. That’s all.”
Crooks also experiences the loneliness of someone who is considered different. Just as he is dreaming of joining George, Lennie and Candy on the farm, Curley's wife reminds him of his otherness. Like Crooks, she also experiences segregation and is treated as an outsider. It is ironic, then, that she should point out to Crooks that he is inferior and that any attempt on his part to mix with the white world will fail. When he tries to get her out of his room, she lashes out at him:
“Listen, Nigger,” she said. “You know what I can do to you if you open your trap?...Well, you keep your place then, Nigger. I could get you strung up on a tree so easy it ain’t even funny.”
At the end of the chapter Steinbeck paints the picture of Crooks alone in his room. Like Candy, who also loses the dream when Lennie accidentally kills Curley's wife, the reader must assume Crooks will remain lonely.