During the 1920s, professional fighter Jack Dempsey—nicknamed the "Manassa Mauler" after his hometown of Manassa, Colorado—was king of the boxing ring. He also was a controversial figure, at once beloved and despised. His participation in one of his sport's most famous and contested matches not only cemented his legend but transformed him into a hero, a mantle he held for the rest of his life.

While still a teenager, Dempsey was boxing as an amateur under the name "Kid Blackie." He eventually turned pro and became the heavyweight champion on July 4, 1919. He knocked out Jess Willard (1881–1968) in the third round, and Willard suffered a broken jaw, two broken ribs, and four missing teeth. The day after his victory, however, sportswriter Grantland Rice (1880–1954) accused Dempsey of evading the military draft. Although Dempsey was found innocent in court, much of the public viewed him...