In John Steinbeck's Of Mice and Men, George and Lennie are described as polar opposites to show how unusual people can be drawn together when they share the same struggles or even the same dreams.
The novel is set in the Great Depression (which began with the Stock Market Crash in 1929). While the story is set in Salinas, California, the Depression spread over the entire country, and people moved around, as go George and Lennie do, to find work (though we learn, too, that George and Lennie also move because of Lennie's inappropriate social behavior).
While Lennie is tall and strong physically, he is like a child mentally. George, on the other hand, is smaller in stature, but he is smart and clever. One seems to complement the other. We learn that George promised Lennie's aunt that he would look out for Lennie, and while it is sometimes a responsibility that wears on him, he does care about Lennie, as we will see at the story's end.
There is some irony in the contrast between the two men. When they first are introduced in the story, one man is following the other. We might think that the taller man would lead and the smaller man would follow, but this is not the case. In truth, the smaller man may not have the physical power that the larger man does, but the smaller man is more powerful with regard to his intellect and survival instincts. Even as they are described, George's features are dark, sharp and accentuated—with a quick step—while Lennie is presented as having "pale eyes" and "a shapeless face," and a heavy, dragging stride.
They had walked in single file down the path, and even in the open one stayed behind the other….The first man was small and quick, dark of face, with restless eyes and sharp, strong features…Behind him walked his opposite, a huge man, shapeless of face, with large, pale eyes, with wide, sloping shoulders; and he walked heavily, dragging his feet a little...
George has even shared his dream of making enough money to one day own his own piece of land, with Lennie; Lennie dreams of caring for the rabbits they will have. In including Lennie in his plan, George extends no only a hand of friendship, but treats Lennie like a part of his own family. While others on the ranch find it odd that the two men travel together, since many people who do not travel as a family (in this time period are alone—which supports the theme of isolation in the book), George and Lennie are connected, which stands out.
The Depression has affected the entire country and has fragmented families and friendships, neighborhoods and businesses. However, there are some, like George and Lennie, who fight this fragmentation by joining together. And where differences might separate some people, here they seem to link these diametrically opposed men in terms of personality, stature and intelligence.