George and Lennie are childhood acquaintences/friends, but not relatives. They are migrant workers trying to fulfill a dream of owning their own land/farm. George has looked after Lennie since Lennie's aunt passed away. Lennie is large with wide shoulders. He has the strength of two men, but the mental capacity of a child. Steinbeck refers to Lennie's hands as paws frequently in the novel. George is much smaller in stature compared with Lennie. He is a good worker, fairly intelligent, and definitely the leader of this duo. He serves in the role of caretaker. The relationship between George and Lennie is almost one of father/son or big brother/younger brother.
Steinbeck describes Lennie as a large man with a shapeless face who walks heavily and whose arms don't swing but hang at his sides. He has pale eyes and walks heavily, dragging his feet as a bear might its paws. He has the lumpen, undefined look of Frankenstein's monster or of a large, lumbering animal. In contrast, George is small and quick, with sharply defined limbs and features. He has strong hands, restless eyes and a slim, bony nose. George's looks indicate he is the brains of the operation while Lennie's show he is the brawn. One might expect the physically bigger and stronger of the duo to be the leader, dominating the pair, but that role goes to George.
While the two men are physical contrasts, they wear the same clothes, which draws them together as one. They both wear denim trousers, denim coats with gold buttons, and shapeless black hats, and have blanket rolls slung over their shoulders. As migrant workers, they are part of an indistinguishable group that people don't look at too closely.
The two men are friends who are down on their luck in the Depression-era economy. George may be the brains of the two and the one Lennie depends on as a leader who makes their strategic decisions, but George is emotionally dependent on Lennie for companionship. He needs someone like mentally handicapped Lennie to look up to him.