Everybody loves an underdog. Upon its release to movie theaters, moviegoers fell in love with an unlikely movie: Rocky (1976). This feel-good film works on two levels—one fictional, and the other factual—as the saga of an obscure "everyman" who gets his shot at fame and realizes the universal fantasy of achieving one's wildest and most improbable dreams.

The film's title character is Philadelphian Rocky Balboa (Sylvester Stallone, 1946–), an inarticulate, faded boxer who is not so much a has-been as a never-was. During the course of the story, Rocky gets to live out a dream: to fight for the world championship against Apollo Creed, the reigning titleholder. Rocky also was the creation of Stallone, an obscure actor who also realized every struggling writer's and actor's fantasy by first penning, then selling, and finally starring in the film.

With Rocky, Stallone rose to acclaim and fame in what was...