Crooks is one of the many characters in John Steinbeck's Of Mice and Men who suffers from loneliness. While many of the others in the novella are lonely in a crowd, so to speak, Crooks is truly isolated from the others by his race as well as by his profession.
Crooks is not allowed to live in the bunkhouse with the others; instead he lives in a little shed connected to the barn. He cares for the horses on the ranch. He is rather bitter and has a chip on his shoulder, which means he is angry at people before they can be angry to him. Obviously this has happened to him before, so now he is always ready for the worst.
Crooks is not friendly, probably because he is out of practice:
Crooks said sharply, "You got no right to come in my room. This here's my room. Nobody got any right in here but me."
Crooks is not happy about Lennie kind of barging into his space, but soon he figures out (with George's help) that Lennie is harmless to him. At one point,
Crooks scowled, but Lennie's disarming smile defeated him. "Come on in and set a while," Crooks said. "'Long as you won't get out and leave me alone, you might as well set down." His tone was a little more friendly.
Clearly this is an indication of several things: no one comes to Crooks's place, Crooks would not be happy about it even if they did, and yet Crooks does warm up a bit when Lennie just ignores (because he does not understand) Crooks's unfriendliness.
Even when he was young, Crooks was an outcast.
"There wasn’t another colored family for miles around. And now there ain’t a colored man on this ranch an’ there’s jus’ one family in Soledad."
He feels his isolation deeply, even here on a ranch which is situated in the middle of nowhere. This is a consistent theme for Crooks, so we are almost as disappointed for him as for George and Lennie when we realize the dream of the farm--with rabbits, of course--will never happen. Crooks's isolation will continue.