Despite being physically over-developed he is mentally under-developed. “I was only fooling, George I don’t want no ketchup…I would leave it all for you...” This shows that he has the brain and personality of a child. This contrast between the developments of his body compared with his mind is the key to the story and, ultimately, the cause of the tragedy. Because of his mental and emotionally limitations, his characteristics and behaviour are child-like. “Lennie, who had been watching, imitated George exactly. He pushed himself back, drew up his knees, embraced them, looked over to George…He pulled his hat down a little more over his eyes, the way George’s hat was,” he sees George as a father-like figure who he looks up to and also tries to imitate and please. George responds to this as a father would, with a combination of threats and promises. It is Lennie’s fear of losing George and the life on the ranch, raising rabbits (this is a theme that Lennie frequently returns to, especially in times of stress for him) that they have planned together that result in the tragedy of the death of Curley’s wife, when Lennie puts his hand over her mouth to stop her crying out for help and accidentally breaks her neck.
Lennie is naïve, trusting, forgetful and unreliable, which is why George looks after his work card and bus tickets, (“Lennie, I aint got mine, I must have lost it. George, I got both of ‘em, you think I will let you carry your own work cards”) but he is obedient to George and tries his best – when he remembers them - to follow the simple instructions that he gives him. He is baby-like in that he cries when upset, but is also easily excited by simple things such as the prospect of having some rabbits to take care of. He likes to touch “purty things”, such as the mouse, the puppy and Curley’s wife’s hair; be he proud of his strength but this strength is also his downfall, because it results in the deaths of these “purty things”.
Steinbeck also portrays Lennie as a violent man throughout the novel by making the character of Lennie unable to control his strength. He has so little control over his own strength that he accidentally kills his puppy, and then minutes later kills Curley's wife. “…a little dead puppy that lay in front of him…and then he put his huge hand and stroked it” this shows that Lennie lacks the understanding that his actions have consequences and he reveals an unintentional violence. He does not understand his own strength; he does not even think to fight back when Curley attacks him, but when he does it is with an immense and uncontrollable force, which makes him a danger to himself and those around him. Despite his naivety, Lennie knows that he does not fit in, for he says, "Well, I can go away, I'll go right off in the hills and find a cave." He is vulnerable in that he cannot avoid the dangers presented by Curley, Curley’s wife, or anyone else, as he only defends himself when George tells him to. He is a character whom Steinbeck sets up for disaster, a character whose innocence only seems to guarantee his unavoidable violence and destruction.
Throughout the novel their friendship is strong as Lennie states, "Because I got you to look after me, and you got me to look after you". From this line we can empathise with Lennie as we all would like a friendship in which both companions look after one another, and want to be loved. Lennie has a distrust of people except for George. Also, Lennie is not always sure about what is right and what is wrong, and he relies upon George to make the decisions for him. Lennie walks his way through life completely unaware to the dangers of the world, holding on to the dream of someday owning a farm with his best friend George.
We do not know a lot about Lennie’s background, but judging by what we are told of his past, he did not have a “normal” happy upbringing. We do not know what happened to Lennie’s family and parents and why he did not live with them, just that he was looked after by his Aunt Clara. Our feelings for Lennie vacillate almost as wildly as his actions at one moment we fear him or he disgusts us, the next he inspires our sympathy when we learn how simply and earnestly he wants to take care of the rabbits, but, when he is out of control he can be frightening, such as when he threatens Crooks. Because is quickly becomes emotional and irrational, but at the same time large and strong, his feelings and lack of logical thought inevitably lead to trouble.
Both Lennie and George are better together than apart. Steinbeck clearly shows how important friends are and how they can support and help each other in different ways. “, Guys like us that works on ranches are the loneliest guys in the world. They ain't got no family and they don't belong no place…: But not us George. Tell about us. : ...well, we ain't like that. We got a future.. : But not us, George, because I... see, I got you to look after me, but you got me to look after you.” From here we can see that Lennie needs George for basic survival; without him, Lennie’s life would not be very long. George on the other hand, needs Lennie for physical protection and a purpose in life.
The sequence of things Lennie kills progresses from small (the mouse) to large (Curley’s wife). Eventually, the largest living thing, namely Lennie himself, is killed by George.
In the tragic world of the novel, description and characterisation are used to prepare us for the inevitable turning point in the story (the death of Curley’s wife) and its sad ending. Despite being his murderer, George does this terrible deed out of love and friendship, not hate. We know that George really does care for Lennie as in the conclusion of the novel, George confesses that “I ain’t angry, I never been angry”; this tells us he had not cared for him out of guilt or because of the promise that he made to Lennie’s Aunt Clara, but that he actually did like him. However, because of the unfortunate combination of Lennie’s physical size and mental immaturity, several mice, a puppy, and one woman pay the ultimate price.