Character Analysis
English Bob is only in the film for a short period of time, but he's symbolically very important. And no; it's not because he insults the president on the Fourth of July.
In the universe of Unforgiven, English Bob is a legendary gunfighter. Various characters suggest that he has been employed by the railroad companies from time to time to shoot Chinese people that may have gotten out of line (railroad companies employed a very large number of Chinese people for projects like the Transcontinental Railroad).
Bob gets wind of the bounty and comes to Big Whiskey, with his biographer in tow (W.W. Beauchamp). He's deadly accurate with a pistol, as he proves during an impromptu pheasant-shooting contest. He's also not one to give up his guns.
When Little Bill confronts him about this, Bob lies. Bill calls it, and disarms Bob, who tries to go on his way. Bill stops him again because he knows Bob has a second smaller gun tucked away. Bill takes this one as well, and proceeds to beat Bob to a bloody pulp.
It turns out that Little Bill and English Bob have a lot of history together, and while Bob is recuperating in a jail cell Bill destroys the sensational and heroic vision of Bob that Beauchamp has already committed to paper. Bob is a drunk, and when he drinks he's prone to horrific violence. Stories about shooting guys to defend a woman's honor, Bill notes, are completely false. Bob is the kind of guy who will shoot an unarmed man, which he once did.
While Bob is in the film to give us a glimpse of Little Bill's vengeful, violent character, he's also in here as a symbol of the Western genre itself, a genre that often resorts to the kind of sensationalizing Little Bill laughs at in Beauchamp's book. Bill strips away the gilded, heroic surface and exposes Bob for what he is in the same way that Unforgiven itself exposes the Western for what it is, a genre that glosses over the complicated ethical issues surrounding violence.
Bonus English Bob symbolism: when Bob is unruffled, he talks in a crisp upper-crust accent. But when he's excited, he speaks in a lower-class Cockney accent. Yup; pretty much everything about English Bob is fake…apart from his skill with a gun.