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In 1975, Chuck Wepner, a journeyman fighter known as the Bayonne Bleeder, was convinced he had snatched the world heavyweight title from Muhammad Ali after knocking the champ to the canvas in the ninth round of a matchup in Cleveland that just about everyone figured would be a cakewalk for Ali.

“I headed back to my corner and said, ‘Start the car — we’re going to the bank, we’re millionaires,’” recalled Mr. Wepner, 80. “And my manager said, ‘You better turn around because he’s getting up.’’

Ali rallied to score a technical knockout over Mr. Wepner, moments before the final bell, but the underdog from Bayonne, N.J., had succeeded in showing the world that he could go the distance with perhaps the greatest fighter ever.

Mr. Wepner’s gutsy performance made an impression on many, including a struggling actor named Sylvester Stallone, who made it the climax of the screenplay he wrote for the 1976 film “Rocky.” The movie went on to win three Oscars, including best picture, and catapulted the young actor to stardom.