Lennie Small is a huge person the mindset of a child. Since he is mentally younger than he looks, he depends on George to survive. Lennie is a kind and caring guy with a big heart. Lennie keeps George sane and gives George something to live for. He doesn’t like to cause problems (for fear of not getting to tend the rabbits) and he loves to pet soft things such as the puppies or the dead mouse. He tends to hurt the things that he touches but doesn’t mean to, because he doesn't know his own strength. He may not be mentally advanced but if you tell him to do something, he will do it which makes him a good worker. He is very loyal to George, and their relationship has been described as a dog and his master (much more prevalent, Steinbeck described Lennie's hands as paws), and a child and his parent.
Lennie has gotten into trouble before, in Weed. Weed was the town George and Lennie worked in before Salinas. Lennie saw a girl's soft dress and was touching it. She wanted him to stop. Confused, Lennie held on to the dress and the girl ran away and said that Lennie raped her (which he didn't). This caused Lennie and George to run away from Weed to Salinas.
Lennie's Aunt Clara adopted him as a child and took care of him. When Aunt Clara died, George was left to care for Lennie.
Because of his strength, Lennie hurts things without knowing it. When he is petting a live mouse and it bites him, he freaks out and squeezes the mouse's head to make it stop. When Lennie had a puppy, he pet it too hard and accidently killed it. When Lennie was touching Curley's Wife's soft hair, she freaked out because he was messing it up. He didn't want to get in trouble, so he covered her mouth and shook her to try to get her to stop screaming. Not knowing his strength, he shook her too hard and accidentally broke her neck and killed her. He then ran back to the brush where George and he had camped the previous night. Later, George found him and shot him out of pity