Robert Cohn as a foil.

"Robert Cohn was once middleweight boxing champion of Princeton," (page 11). Hemingway chooses for the reader's first image of Cohn to be one of a fighter. In the novel, he fights for many things. But one thing that is always true is that he is fighting against some other character. Cohn is not a typical foil character who goes against one character. Cohn, at some point in the novel, goes against just about every major character. He loves Brett, which causes him to go against Mike. They get in numerous verbal altercations over his obsession with Brett. He also physically attacks Jake on page 195.
Throughout the entire novel, Cohn spends his time foiling one character or another. Hemingway uses this type of foil not only to contrast other characters, but also to epitomize the extreme personalities in society that he does not approve of. Cohn serves as a character that can be molded into many types of people that are easy to understand because they are common in society. Hemingway uses this unique type of foil to bring a timelessness to the novel and its characters.