Lennie Small is a large, physically intimidating migrant worker who is a static character. Despite his size, Lennie has intellectual disabilities, resulting in a childlike innocence. He shares a close friendship with George and dreams of raising animals on their future farm.

Slim is a tall, skilled skinner on the ranch respected by his peers as the "prince of the ranch." He confidently stands up to Curley and gains the men's respect. Slim is a friendly, trustworthy figure to whom George confides about his relationship with Lennie.

Candy is an older ranch handyman with an uncertain future due to his physical disability, having lost a hand. He finds hope in George and Lennie's dream of owning a farm and offers his savings to be part of it.

Curley is the short, aggressive antagonist of the novella and the boss's son. Known for his inept management and confrontational nature, he mistreats the workers, boasts of his boxing prowess, and is suspicious of his wife's interactions with other men.

Curley's wife is the only woman on the ranch, searching for attention and companionship due to her loneliness and unhappy marriage. Her unfulfilled dreams of becoming a movie star contribute to her dissatisfaction with life on the farm.

Crooks is the only Black man on the ranch, living in isolation due to racial segregation. Although he outwardly insists on his solitude, Crooks craves company and briefly dreams of joining George and Lennie's farm.

Carlson is a large, strong ranch hand known for his insensitivity. He owns a Luger and encourages the mercy killing of Candy's old dog. Carlson fails to understand the emotional struggles of others, as exhibited in the novella's closing scene.

Whit is a younger ranch hand whose body shows signs of hard labor. He admires Slim and views him as a leader. Whit represents youthful optimism, contrasted by the grim reality of the other laborers' unfulfilled dreams.