He represents the romanticized figure of the American West as it appeared in dime-store novels, standing in stark contrast to the brutal, raw reality of the period as represented by Eastwood's William Munny. The beating and subsequent banishment of English Bob symbolizes the de-mythification of the West which is one of Unforgiven's main themes.
This is obvious to anyone who actually tries to understand the movie instead of looking at it purely on its surface.