Slim is called "the prince of the ranch." Even though his official rank is lower that the bosses son, it is Slim that the men respect.When Carlson wants to shoot Candy's dog, Candy waits for Slim's implied approval before he lets Carlson shoot his dog. Slim is also the character to whom George reveals the most to about Lennie. In the end, it is also Slim who comforts George and understands George's actions towards Lennie.
Crooks is the only Black man on the ranch. Even though he has been there a long time, he is separated from the rest of the men because of his skin color. He must stay in his own room and read books for company. Only the child-like Lennie sees no difference between Crooks and the other men at the ranch. However, even Curley's wife treats him with disdain when she threatens to have him lynched. Thus, Steinbeck is one of the first twentieth century writers to deal with racial segregation in California, which never allowed slavery, yet the attitudes towards Black men were the same as in the South.
Curley is a man, who just like his name, is wound too tightly and he is too ready to spring into action. He seems bitter that he is not physically larger and so he uses his position as the bosses son to push people around, especially his wife and Lennie, His role is to be the irritant that everyone hates, yet everyone must respect. He is also one of the main reasons Goerge kills Lennie, to free Lennie from the probable vindictive actions of Curley.