I would argue that other than killing Gatsby, George Wilson does not have an "effect" on others, and that is his problem. Even Fitzgerald's physical description of his with his ashen hue and all-encompassing paleness (including his hair) illustrates George's lack of significance in any setting. He fades into the background literally and figurative. His wife orders him around; he can't get a straight answer from Tom Buchanan about the car; he even lives and works in the Valley of Ashes, a place of grey desolation, where he has no opportunity to effect any change or affect anyone.
Even at the novel's end, when George hopes to at least have an effect on his wife's killer by getting revenge upon him, he kills the wrong person and never achieves his own desired effect.
At the inquest following all of the deaths, no one stands up for George, and it is as if he never existed by the time the hearing is finished.
In the end, Fitzgerald's characterization of George perfectly represents his belief that the lower and middle class of American society do not have a chance at obtaining the American Dream and that their very existence has no effect upon Old Money Society. They are discarded like trash while the rich run off to some new location, hobby, or mistress (as do Tom and Daisy).
George plays the role of a cuckold. The word is derived from the cuckoo bird, which lays her eggs in other birds' nests. So, the husband of a cuckoo (Myrtle) is called a cuckold because he is duped by a wife who sleeps around. The irony, of course, is that everyone knows the cuckoo is unfaithful, except the cuckold. Historically, a cuckold is the worst epithet a man can be called. Like George, cuckolds feel extremely jealous and lash out in revenge in response to feelings of inferiority.
Myrtle describes him as such:
I married him because I thought he was a gentleman...I thought he knew something about breeding, but he wasn't fit to lick my shoe.
She has bought into Tom's racist beliefs, describing her own husband like an animal--an inferior creature ("breeding" and "lick").
His impression is not much better with others. George is described by Nick thusly:
"..he was a blond, spiritless man, anemic, and faintly handsome. When he saw us … hope sprang into his light blue eyes.”
George finally discovers that his wife is cheating on him when it is painfully obvious, when he sees her running out to (what he thinks is) her lover's car. After she is killed, he avenges Myrtle's death, but he mistakenly kills the wrong man, Gatsby, instead of Tom. So, George is symbolic of Gatsby's sordid past--one of lies, denial, and falsehood--catching up with him.
George also affects the way Tom feels about himself. George, a mechanic, is preoccupied with cars. He asks Tom repeatedly to sell him one of his cars. Tom refuses, which makes him feel superior to the underclass mechanic.
George is so preoccupied with cars, in fact, that he fails to discover the real identity of Myrtle's lover. It is important to note that George's jealousy as a cuckold is not sexual at all--it is purely materialistic. He only becomes aware and jealous when both Myrtle and the car come together. Such was the importance placed on socio-economic status in the 1920s, according to Fitzgerald. So, George is a symbol of the proletariat, the working class who, no matter how hard they work, will always be victimized by the rich.