Although he does not talk about himself in a direct manner, in describing others, Jake reveals much about his own feelings and thoughts while struggling with his love for Lady Brett Ashley, impotence and the moral aftermath of the war. Bill Gorton is an American war veteran and close friend of Jake. They share a strong bond although they have different ways of coping with the cruelties of war which Bill deals with using humor. Jake's love interest, Lady Brett Ashley is a beautiful British socialite who takes refuge in alcohol. Despite being in love with Jake, she does not want to embark on a committed relationship with him. In fact, she does not commit to any of the men she becomes involved with although her independence does not bring her happiness either. In many ways her life, similarly to those of many other members of the Lost Generation, lacks personal fulfillment and a clear purpose. Robert Cohn is a wealthy Jewish-American writer, a nonveteran who manages to keep his ideals of love and fairness intact even after the war; in fact, it is his idealism that establishes him as the opposite of Jake and his friends. Pedro Romero also represents Jake's opposite....

He is a young, charming and talented bullfighter who exudes dignity and self-confidence. In addition, Pedro's life has meaning and aim thanks to his passion for bullfighting; in this sense, in a world dominated by aimlessness and bitterness in which masculinity has been redefined Pedro manages to remain a figure of strength and integrity. This contrast also helps readers get a more profound understanding of the Lost Generation with its loneliness, failure to communicate, and emptiness.
These characters live in a vacuum of values which does not allow them to experience personal fulfillment. Society as a whole has lost its innocence thus these characters become its best representatives. To a large extent, the Biblical quotation that the novel opens with, "One generation passeth away, and another generation cometh; but the earth abideth forever" (Ecclesiastes 1:4) best explains the connection between characters and title in the sense that it expresses the constant renewal of the search for meaning that occurs with each new generation.

Source

Hemingway, Ernest. Fiesta: The Sun Also Rises. Simon & Schuster Adult Publishing Group, 1995.