George Milton, a migrant laborer, is like a mouse: "small and quick, dark of face, with restless eyes and sharp strong features. Every part of him was defined: small, strong hands, slender arms, a thin and bony nose." George has brains and ambition.
George is a complex character because he has not accepted his lot in life. He dreams. He dreams of owning his own farm. He is not satisfied migrating from ranch to ranch. He is determined to make it.
George takes care of Lennie. He has a good heart:
George is loyal in his friendship with Lennie, and he is also remarkably pure of heart.
He would not desire for anything to happen to his companion Lennie. Sure, he does get frustrated with Lennie form time to time, but that is due to his true concern for Lennie. George sacrifices his own happiness for Lennie. When Lennie is in trouble and on the run, George is in trouble and on the run as well.
George had no choice but to shoot Lennie. He did so to keep Curley from torturing Lennie. George ends his own dream when he shoots Lennie. He has Lennie's best interest at heart. Now, Lennie will not have to hang. George takes good care of Lennie, even in death.
Of course, George will be lost without Lennie. He will suffer a great loss. George deeply cared about Lennie. He had sacrificed his own freedom to care for Lennie. Without Lennie, George will lose his will to dream:
When George is driven to shoot Lennie after Lennie accidentally kills Curley's wife, he destroys his own dream, too. Its fulfillment is doomed by insensitive materialists. Along with the destruction of his dream, George loses the chance to become a better man.