One of the greatest stories of an underdog ever. The main character, Rocky Balboa played by Sylvester Stallone, went from being a poor, inner-city Philadelphia club fighter to the world boxing champion, making him go from rags to riches in a short time. He meets his love, Adrian in a pet store and marries her in Rocky 2. They go on to have a son and name him Rocky Jr. In the last film, Rocky 5, he "adopts" a young kid and shows him the ropes of boxing, only to become the object of his jealousy and has to defend himself in a street fight, proving he is the greatest fighter of all time.
Rocky is probably the greatest series of sports movies of all time.