One of the earliest references to Carlson occurs in reference to Curley's wife. Carlson is one of the men for whom she is said to have given "the eye."
We are also told that Carlson is a "big man" and "thick-bodied." He also seems to be a friendly man as he makes a gentle joke about Lennie Small not being "small at all."
On the other hand, Carlson is the one who forces Candy to get rid of his old dog and Carlson is the one who shoots the dog to put it out of its misery. Thus, Carlson's actions anticipate those of George with Lennie at the end of the novel. George even uses Carlson's gun to kill Lennie.
Finally, we also note that Carlson is not afraid of Curley. When Curley comes into the bunkhouse looking for his wife, Curley challenges Carlson to fight. Carlson responds fearlessly:
You’re yella as a frog belly. I don’t care if you’re the best welter in the country. You come for me, an’ I’ll kick your God damn head off.”
Thus, Carlson seems like a decent fellow. He is certainly no weakling or coward and his actions with respect to Candy's dog foreshadow what happens between George and Lennie at the novel's conclusion.
In Chapter 2, Steinbeck directly characterizes Carlson as a powerful man with a big stomach when he enters the bunkhouse. Carlson then jokingly mentions that Lennie "ain't very small" and suggests that Slim give Candy one his pups so Candy can get rid of his old dog. His comments indirectly characterize him as a light-hearted, thoughtful person.
In Chapter 3, Carlson comes into the bunkhouse and yells at Candy about his smelly dog. Carlson then tries to convince Candy to put his dog out of its misery. After Slim gives the okay to shoot the dog, Carlson apologetically tells Candy that the dog won't feel a thing. Carlson's comments and actions indirectly characterize him as a reasonable, sympathetic individual. He understands that the dog is important to Candy so he tries his best to assure him that the dog won't feel a thing.
Later on in the novella, Carlson ridicules and threatens Curley for attempting to scare Slim. Carlson's response to Curley's behavior depicts his brash, daring personality. Carlson is not afraid of Curley and even challenges him to a fight. After Curley finds out Lennie killed his wife, Carlson offers his assistance by grabbing his Luger. Carlson is not afraid of violence and is definitely a man of action throughout the novella.