In my opinion, George is the most dynamic(changing) character in the story. He has great care for his friend Lennie although he is often slow to show it on the outside. He has been Lennie's father figure for years and this storyline demonstrates the problem of such wear and tear on a relationship.
Lennie, his side-kick grows, but because of his mental disability this happens slowly. His strength is incomprehensible to him and caring for soft things gets him in trouble.
Most characters don't grow much throughout this story which I think was indicative of these times. Steinbeck carefully portrays the rut that this ranch-hand kind of life created. It demonstrates lonliness and low ambition.
Curley has reason to encounter a drastic change when his wife dies. Throughout the story, from the on-set of Lennie (a big man that threatens Curley's little man complex), to the constant wonderings about the whereabouts of his wife and eventually to the accidental death of his wife, Curley undergoes a transformation. He began with curiosity, moved to distrust, and eventually rage.
In the exposition of John Steinbeck's Of Mice and Men, old Candy, the disabled ranch hand meets George and Lennie as he sweeps out the area where the two men will sleep. When George becomes concerned about the can of lice killer on the box shelf, he asks Candy, "What the hell's this?" The "old swamper" is hesitant, shifting his broom, and haltingly explains that the man was clean. As George demands to know if the bunk is infested, Candy haltingly tries to explain.
But, he does strike up a conversation with the two men about the "stable buck" and the boss's being upset that George and Lennie were not ready to work in the morning. When the boss arrives, Candy "shuffled past the boss and out the door." Clearly, Candy's position is lowly and he is very subservient to the boss as well as anyone in authority because he is worried about what he will do without his job. His is a life of "quiet desperation" as Thoreau wrote in his Walden. All alone in the world with only an aged dog that is decrepit, Candy is insecure at the bunk house. He offers little resistance when the callous Carlson takes his aged and decrepit dog to kill it.
Bereft after losing his dog, Carlson withdraws until George includes him and his $350 in their "dream" of owning their own ranch. Given hope for his old age, Candy feels empowered by his new friendships; he tells George he should have had the courage to shoot his dog himself, and he talks back to Crooks one night when Crooks refuses to let Lennie enter his barn. Then, Candy warms a little, although he is rather embarrassed to enter Crooks room when invited. Yet, he compliments the room to Crooks. During the day, he sits and calculates how the men will buy their ranch.
When Curley's wife enters the barn, Candy boldly scolds her:
He said accusingly, 'You gotta husban'. You got no call foolin' aroun' with other guys, causin' trouble.'
When she asks about her husband's hand, Candy diplomatically says that he had it caught in a machine. Undeterred by her laugh, Candy repeats the phrase, " Got it caught in a machine. As Curley's wife becomes somewhat antagonistic, Candy's face reddens, but before she is finished talking, Candy "had control of himself." He tells the woman to go, and as she looks from one face to another, "they were all closed against her."
Candy has gone from being a intimidated broom pusher in the bunk house to a respected member of the small group of men, thus serving to further Steinbeck's theme of the brotherhood of men and it benefits.