We know he reads books because he read the California civil rights code. In conclusion we are able to learn a great deal about Crooks in these pages all of which is there to remind us of the awful thing which was segregation. He lives by himself because he is the only black man on the ranch.
Steinbeck has included Crooks to represent black people in America and show how they were treated. Perhaps Steinbeck did this to show the reader the simplicity of the lives of the migrant workers.
We think crooks is a character used by Steinbeck to show the effects of discrimination. This portrays the simple nature of the bunkhouse and it's only purpose: housing the ranch hands. Despite his pride, Steinbeck shows that he is actually very lonely and wishes that he had more company.
Crooks is the stable hand who takes care of the horses and lives by himself because he is the only black man on the ranch. Firstly, that Crooks is like an animal because he sleeps next to the barn, also he cannot be important if he lives in a shed. Prejudice isn't simply a characteristic of the white ranch hands or the daughter-in-law of the boss; it is a human characteristic, and Crooks needs to feel superior to someone also.
It also adds to the idea of it being old.