John Steinbeck wanted to write a story about two farm laborers who share a dream of owning their own farm and not having to slave for others for a bare existence. But he must have realized that there was something a little odd about such a relationship. It has always been the natural pattern for a man and a woman to own a farm. If two men were to live together on a farm, some people would suspect that they had a homosexual relationship. A number of questions posted in eNotes have actually asked whether George and Lennie are gay. No doubt Steinbeck would have been glad to write a story about a man and woman who dreamt of owning their own farm, but he could not make them itinerant farm workers because a woman could not do heavy farm labor or sleep in bunkhouses with a bunch of men.
So Steinbeck had to invent a reason why these two men could live together and share ownership of a farm but not be gay. He thought of making one handicapped and the other his caretaker. But if Lennie were physically handicapped he couldn't be an itinerant farm laborer. Then Steinbeck must have come up with the idea of making Lennie mentally handicapped. To make up for this mental weakness, Steinbeck made him exceptionally strong. He could do the work of three men in the fields, and he would be an asset to George if they ever got that farm.
George, of course, would have to be shaped into the kind of character who would accept long-term responsibility for such a burden as Lennie. George made a promise to Aunt Clara which she had no right to ask. George is a healthy, intelligent, capable man who should be married and raising a family; instead, he is stuck perhaps for life with a retard who is always getting into trouble.
According to the Introduction to Of Mice and Men in the eNotes Study Guide, Steinbeck intended to convert his story into a play and did so the same year the novella was published. He could see the advantage of having a character in a play who was mentally retarded, because his buddy would have to keep explaining things to him. In a play the exposition has to be conveyed through dialogue, and having George explaining and repeating everything to Lennie makes it easy to convey information to the audience.
Steinbeck is conspicuously defensive about the relationship between George and Lennie. The boss who hires them is instantly suspicious.
"I said what stake you got in this guy? You takin' his pay away from him?"
"No, 'course I ain't. Why ya think I'm sellin' him out?"
"Well, I never seen one guy take so much trouoble for another guy. I just like to know what your interest is."
Slim is also curious.
"Funny how you an' him string along together."
"What's funny about it?" George demanded defensively.
"Oh, I dunno. Hardly none of the guys ever travel together. I hardly never seen two guys travel together. . . . It jus' seems kinda funny a cuckoff like him and a smart little guy like you travelin' together."
Note how George "demanded defensively." Here Steinbeck has George give Slim the story about Aunt Clara.
"It ain't so funny, him and me goin' aroun' together. Him and me was both born in Auburn. I knowed his Aunt Clara. She took him when he was a baby and raised him up. When his Aunt Clara died, Lennie just come along with me out workin'. Got kinda used to each other after a little while."
Steinbeck invented the best plot he could think of to illustrate his thesis and to dramatize the lives of itinerant farm workers in the 1930s.
Lennie and George are two men that are pretty much best friends. In chapter 3, George explains to Slim,"Him and me was both born in Auburn. I knowed his Aunt Clara. She took him when he was a baby and raised him up. When his Aunt Clara died, Lennie just come along with me out workin'. Got kinda used to after a little while". The relationship between the two was peculiar, but when it came down to it-George grew to love Lennie-no matter how dumb he was.