In Of Mice and Men, George plays the following roles:
Traveling Companion, Caregiver, and Dreamkeeper for Lennie. Early in the novella, George must care for Lennie's survival and basic needs (food, shelter). The two are migrant workers, and while George must find the jobs, Lennie is a capable worker. Also, George must remind Lennie of the Dream Ranch, and he tells the story of how Lennie will tend the rabbits. George also perpetuates the dream for Candy.
Rogue Mercy Killer. Later in the novel, George must resort to secret crime (stealing Carlson's gun) in order to prevent Lennie from becoming the victim of vigilante revenge. He re-tells the dream to Lennie and shoots him, giving him a somewhat quick and relatively painless death. Throughout, George has used the Dream Ranch tale in order to pacify Lennie, and one wonders if he ever believed it was possible.
George has been through a lot in his life, and the hardship of the Depression and his transient nature as a migrant worker has made him suspicious of everyone but Lennie. We see this early in the book in his conversations with Candy about the bunkhouse, and his anger at the bus driver who leaves them off too soon, as well as his first exchange with Curley.
"I seen hunderds of men come by on the road an' on the ranches, with their bindles on their back an' that same damn thing in their heads. Hunderds of them. They come, an' they quit an' go on; an' every damn one of 'em's got a little piece of land in his head. An' never a God damn one of 'em ever gets it.
We see George start to warm up as the story progresses, and he becomes more confident in his job and his surroundings. When he decides to go in on buying the small farm with Candy and Lennie, we see the hope take over and George becomes positively friendly and happy. Of course, it is short lived, but George's personality mirrors his current situation, including after the tragedy at the end and he reverts to his former, sullen self.
“With us it ain’t like that. We got a future. We got somebody to talk to that gives a damn about us. We don’t have to sit in no bar room blown’ in our jack jus’ because we got no place else to go. If them other guys gets in jail they can rot for all anybody give a damn. But not us.”
he always took care of Lennie but then he committed an illegal act.