Why does George trust Slim?

In Chapter 2, when Slim first appears, the narrator describes him as someone who has earned the reputation of a respectable, authoritative person:

There was a gravity in his manner and a quiet so profound that all talk stopped when he spoke. His authority was so great that his word was taken on any subject, be it politics or love. 

Slim notes that it is odd that George and Lennie travel around together. In Chapter...

In Chapter 2, when Slim first appears, the narrator describes him as someone who has earned the reputation of a respectable, authoritative person:

There was a gravity in his manner and a quiet so profound that all talk stopped when he spoke. His authority was so great that his word was taken on any subject, be it politics or love. 

Slim notes that it is odd that George and Lennie travel around together. In Chapter 3, George defends his and Lennie's partnership. Slim agrees with George that the typical worker keeps to himself and this is a lonely life: 

You know how the hands are, they just come in and get their bunk and work a month, and then they quit and go out alone. Never seem to give a damn about nobody.

After hearing this, George tells Slim about his history with Lennie. He even confides in him about the event in Weed which made them leave. Lennie comes in, fawning over a puppy, and Slim says of Lennie, "He's jus' like a kid, ain't he?" Slim recognizes that Lennie is as innocent as a child. Slim is fair and understanding. This is why George trusts him. George recognizes Slim's wisdom and authority. When Lennie crushes Curley's hand, Slim commands Curley to tell his father that he injured his hand in a machine. Curley agrees. Slim has protected Lennie in this way and George appreciates it.