I will discuss Slim’s function in the text. Aside from George and Lennie’s strong friendship in the story, the ranch hands have little connection among themselves beyond superficial interactions. Slim and Candy are the only two of all the workers who actually seem to understand the relationship between George and Lennie.
Slim mostly serves as an example of the ideal migrant worker. He is noble and respected, well-liked and generous. George almost immediately strikes up a kind of friendship with Slim, even though he doesn’t plan on staying at the ranch for an extended period after he and Lennie earn their “stake.” Slim gives Lennie a pup and remarks on the man’s superior work ethic and strength. Slim tells George that Lennie has no “meanness” in him, which shows that he has a favorable opinion of Lennie.
Besides George, Slim is the only member of the party who searches for Lennie, after Curley’s wife dies, who is sad over the tragic but necessary killing of Lennie. Carlson, another ranch hand observing Slim and George’s somber mood, asks, “Now what the hell ya suppose is eatin' them two guys?” This statement shows that most men in this text lack an emotional connection to other human beings. Their lack of empathy is the norm, so Slim’s ability to share George’s sorrow shows that he is an exception to this norm. Slim is an idealized version of the noble ranch hand who possesses the emotional intelligence to understand the suffering that exists around him.
Based on this, one might argue that Steinbeck includes Slim as a foil to those who represent the cruel isolation of migrant life.