Slim is first described as “a big, tall, skinner” and we learn that George and Lennie are going to be on his team (ch 2). Slim is also described as “a nice fella.” One way that Slim shows power is by addressing Curley’s wife as “good-lookin” when most of the men are afraid to talk to her.
[He] moved with a majesty achieved only by royalty and master craftsmen. He was a jerkline skinner, the prince of the ranch. (ch 2)
He is respected because of his strength, but he has a gravity to his speech and his word is accepted on any subject, including politics.