In Chapter 3 of Of Mice and Men, the reader learns that Lennie, George's friend, has the strength of a Samson, and that George is able to control Lennie, at least at certain times.
In the bunkhouse as Slim and George play cards, they talk. George tells Slim that Lennie, who enjoys petting one of Slim's puppies, is a bit of a nuisance, but his Aunt Clara asked George to look out for Lennie before she died. He tells Slim,
"After Aunt Clara died, Lennie just come along with me out workin' Got kinda used to each other after a little while."
Further, George reveals that he used to play jokes on Lennie; however, one time Lennie nearly died after he told Lennie to jump into a river because Lennie could not swim. George had to pull Lennie out of the water, but Lennie
"...was so...nice to me for pullin' him out....Clean forgot I told him to jump in. Well, I ain't done nothing like that no more."
George also tells Slim that Lennie is a "nuisance," but he is used to the company.
Later, when Curley comes into the bunk house looking for his wife, Slim becomes angry with him. Curley, then, turns his wrath upon Lennie, who smiles because he has been thinking about their dream of a ranch. But, Curley punches Lennie with his left hand and then he smashes him with his right hand. "George," he calls out, "Make 'um let me alone." So, George orders Lennie to "get him" and not let Curley hit him. As Curley's fist swings for Lennie, Lennie crushes his right hand. When Lennie holds on and Curley screams in agony, George orders him to release Curley's crushed fist. Lennie obeys George, as he usually does.