When all men go to the town and Lennie goes to visit his puppy, who does he visit in Of Mice and Men?

Lennie talks to Crooks while the men are in town.

George and the other men go into town to spend their paychecks, and Lennie stays behind.  He goes into the barn to visit the puppies.  There he finds Crooks, the black stable hand.

Lennie flapped his big hands helplessly. "Ever'body went into town," he said. "Slim an' George an' ever'body. George says I gotta stay here an' not get in no trouble. I seen your...

Lennie talks to Crooks while the men are in town.

George and the other men go into town to spend their paychecks, and Lennie stays behind.  He goes into the barn to visit the puppies.  There he finds Crooks, the black stable hand.

Lennie flapped his big hands helplessly. "Ever'body went into town," he said. "Slim an' George an' ever'body. George says I gotta stay here an' not get in no trouble. I seen your light." (Ch. 4)

Crooks is used to being alone.  Most of the ranch hands do not fraternize with him, because he is black.  This is why he lives alone in the tack room instead of in the bunk house with the other men.  Crooks is also something of a permanent resident at the ranch, where the other men are migrants and go from ranch to ranch following work.

Crooks tells Lennie he isn’t wanted.  He tells Lennie that he does not belong in the barn since he is not a skinner.  Lennie tells him he is there to see the puppy.  Soon, it is clear to Crooks that Lennie is not like the others.

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. "All the boys gone into town, huh?" (Ch. 4)

Crooks and Lennie are both outcasts and they are lonely.  Lennie seeks comfort and companionship with the puppies, and Crooks finds it in Lennie.  He is able to let his guard down because Lennie sees him as a person and not a black man.

Unfortunately, Lennie soon kills the puppy and then accidentally kills Curley’s wife, so it is not a long friendship.  Lennie is childlike, does not know his strength, and seems unable to control himself.