Lennie Small is a huge, extremely strong man who is mentally handicapped. He was raised by his Aunt Clara. George was a friend of the family, and after Aunt Clara died, Lennie and George began to work together, and a strong friendship developed between them. Lennie is a gentle, innocent person. He can get angry if sufficiently provoked, but he is not malicious. Lennie realizes he does not understand people and social situations as well as other people do. Because of this, and because he is so strong, he can accidentally get into trouble. Lennie has a great need for companionship and strongly values his relationship with George. He loves petting soft animals, like mice, rabbits, and puppies, but because of his enormous strength, he can accidentally kill these creatures. Lennie is fixated on the dream of obtaining a small farm with George and tending rabbits. Because of his brute strength and clumsiness in social situations, however, Lennie inadvertently contributes to the destruction of his own dream.
George Milton is a small man with a sharp mind who is good at planning and has insight into social dynamics. George was friends with Aunt Clara and Lennie, so when she died, George and Lennie began to work together. At first, George played jokes on Lennie, but he soon realized that these jokes were cruel and dangerous, so George stopped teasing Lennie and formed a strong friendship with him. Like Lennie, George has a strong need for friendship. He realizes that his friendship with Lennie sets them apart from most other migrant workers. George and Lennie look out for each other, whereas other migrants have no one to care for them. Also like Lennie, George dreams of obtaining a small farm and often tells Lennie about these plans. George can get frustrated and annoyed at Lennie and his obtuseness, but this annoyance always gives way to gentler feelings. George is fully aware of the dynamics that could lead to the ruin of his and Lennie's dream, but even so he cannot prevent them from happening.
Curley's wife is a young, attractive woman and the wife of the boss's son. She is flirtatious and constantly tries to get affection from men. She does not like her husband and so does not look to him for the attention and affection she craves. She believes her strongest attribute is her appearance because it has gotten her attention in the past. She feels stuck at the ranch and resents her situation. Because of this, she flirts with and teases the male workers, knowing that it makes them uncomfortable. Her need for affection draws her to gentle, slow-witted Lennie. She has no idea of the danger he represents, which leads to her death.
Curley is the son of the boss of the ranch and considers himself an accomplished lightweight boxer. Curley is a small man and feels insecure because of his size. As a result, he constantly tries to prove his manhood by picking fights with larger men. Also because of his insecurity, he suspects men of flirting and sleeping with his wife. This situation is made worse by his wife's blatant flirtations. Curley has a quick temper and can lash out violently. He picks a fight with Lennie and gets his hand crushed as a result. Later, he exacts revenge on Lennie.
Slim is a skilled ranch hand and perhaps the most respected man on the ranch. He forms a friendship with George and recognizes Lennie's limitations and good intentions. He steps forward to protect Lennie from Curley after Lennie crushes Curley's hand. At the end, he comforts George for shooting Lennie, telling him it was something he had to do.
Candy is an old man who has worked at a ranch near Soledad, California, for many years. His right hand was torn off during an accident. He has an old sheep dog that has been his companion since the dog was a puppy. Candy sweeps out the bunkhouse, about the only job he is fit to do at the ranch. Candy fears being cast out when he can no longer sweep the bunkhouse, leaving him on his own in his old age. When his dog is shot because it is old, useless, and smelly, Candy's fears intensify. Candy has had the foresight to save some money, however, and he offers a partial payment on the small farm that George and Lennie want to buy if he can stay on the farm with them and do odd jobs. Therefore, George and Lennie's dream also becomes Candy's dream. Candy is crushed when this dream falls apart.