Humphrey Bogart's last film.
Primo Carnera unsuccessfully sued the film's makers, claiming it damaged his reputation for implying that he was involved in fixed fights. Carnera's career is one of the biggest mysteries in boxing, as many of the sport's historians believe that, without Carnera's knowledge, his managers paid most of his opponents to throw their fights.
According to Hollywood urban legend, Bogart was so sick during filming that his voice had to be re-dubbed by an impersonator. In truth, though, the voice heard in the film is indeed Humphrey Bogart's own voice.
Former heavyweight champion Max Baer plays Buddy Brannen, the boxer who ends Toro Moreno's career in the film's climax. In reality, Baer also ended Primo Carnera's championship run, knocking Carnera down 11 times in 10 rounds in a brutal beating. As the film is based on Carnera's career, Baer therefore essentially played himself in it.
Loosely based on the career of fighter Primo Carnera.
The character of Eddie Willis is based upon the career of writer and event promoter Harold Conrad.
Toro Moreno's manager, Luis Agrandi, is said to be from Argentina, but his accent in speaking Spanish to his fighter is obviously Mexican, not Argentine.