What are the roles and importance of Robert Cohn in Ernest Hemingway's novel The Sun Also Rises?

Robert Cohn serves a number of important functions in
Ernest Hemingway’s The Sun Also Rises, including the
following:

• He is the object of derision by many
  of the other characters, and thus he acts as a kind of foil to many of them, even though
  in some ways they are no more appealing or attractive than he
  is.


• He is Jewish, and so he gives some of the other
  characters a chance to vent their odd anti-Semitism.


• He,
  like many of the other men in the book, is attracted to Brett Ashley and is somewhat
  desperate in his obsession with her. Thanks to his presence, she has a chance to display
  her personality, which he and others seem to find
  appealing.


• His obsession with Brett provides an
  opportunity for other males in the book to display their jealousy and
  competitiveness.


• He is one of the males who particularly
  seems to contrast with Pedro Romero, who seems to embody Hemingway’s (and Brett’s) ideal
  of male perfection.


• He is a source of much conflict in
  the book and thus contributes to the drama of its
  plot.


• Reactions of other characters to Cohn reveal a
  great deal about their own personalities and
  temperaments.


• He comes from a wealthy family and thus
  symbolizes the role that wealth will play as a major theme in the
  book.


• He has been divorced, and divorce is another major
  theme of the novel.


• He has made, lost, and regained
  money, thus symbolizing the fluctuating financial fortunes of a number of other
  characters.


• He gives a number of the other characters a
  chance to display smug superiority. It is possible to argue that one of the purposes of
  the book is to mock such unmerited pride.


• He is highly
  insecure, but then so are many of the other characters (including Brett). He thus
  symbolizes one more major theme of the novel.


• His egotism
  is somewhat comic, but the same can arguably be said of other characters, including
  Brett.  Early in the novel, for instance, the narrator says of Cohn’s divorce, which
  results from his wife leaving him,

readability="7">

As he had been thinking for months about leaving
his wife and had not done it because it would be too cruel to deprive her of himself,
her departure was a very healthful
shock.