In Of Mice and Men, Slim is highly-respected by the men on the ranch. To find evidence which supports this idea, take a look at chapter 2. When the triangle sounds for dinner, for instance, notice how Carlson lets Slim go before him:
Carlson stepped back to let Slim precede him.
By letting Slim go first, Carlson is acknowledging Slim's elevated status on the ranch. This suggests that Carlson has a lot of respect for Slim and his position.
Similarly, in chapter 3, Slim tells Candy that he must shoot his dog, and Candy accepts his decision without question. As we see in the text, "Slim's opinions were law," meaning that if Slim decides something must happen, then the other men obey.
Slim is not only respected because of his strength and experience, he is also respected because of his character. Notice how open and welcoming he is towards George and Lennie, for example, which provides a strong contrast with Curley. By being fair and open, Slim has reached a level of respect which surpasses all the other men on the ranch.