Between Slim initially calling Lennie a "cuckoo" and being the one who makes the final decision to put down Candy's dog, what do these reveal about Slim's character?
The original question had to be edited. I would suggest that Slim is not necessarily a bad guy. Slim is an embodiment of a man of action. He recognizes what needs to be done and when all others seem to be impotent in action, he is the one who recognizes the need for it. Slim is shown to be the type of man who is honest in his assessment of the situation and one who "calls it as he sees it: "His ear heard more than was said to him, and his slow speech had overtones not of thought, but of understanding beyond thought." In these ideas, Slim is shown to be one who strives not to be the most beloved and the most favorite of the ranch hands. Rather, he fully understands that there is a need to take action and sometimes, that action might not be pleasant. I think that his initial judgment of Lennie has to be balanced out with how he ends up seeing him, as evidenced in Chapter 3. Slim understands that there is a good heart in Lennie. Slim understands the capacity of the truth in life. Within these constructions, one can see that Slim's dedication to understanding the truth behind action and comprehending that living is not defined as a "popularity contest" as much as it is something in which individuals must act and do what needs to be done. It is here where I think that the initial statements about Lennie and his advocacy for putting down Candy's dog might not necessarily reflect the full scope of his character.