The last Republic serial made about a superhero — and the most expensive serial that they would make — Captain America is about the hero in name only. Republic was famous for making major changes in their adaptations, but these ones get crazy.
Cap isn’t Steve Rogers, he isn’t in the army, there’s no Bucky, he doesn’t fight any Nazis, he uses a gun instead of his shield and he never got the Super Soldier Syrum. Instead, he’s District Attorney Grant Gardner.
Therte are a few different theories.
Jim Harmon and Don Glut believe that this was going to be a sequel to 1940’s Mysterious Doctor Satan, which had already substituted the invented superhero The Copperhead for Superman after Republic lost the rights to Paramount to make that serial.
Film restoration director Eric Stedman has the theory that since Republic had made two serials the Fawcett Comics characters Captain Marvel and Spy Smasher, this serial was meant to start Mr. Scarlet, whose alter ego is District Attorney Brian Butler.
After multiple scientists and businessmen — who all went on the same Mayan exploration — kill thenselves and are found holding a scarab, the police ask District Attorney Grant Gardner to bring in Captain America and seeing as how they’re the same person, that’s easy. The bad guy? Lionel Atwill, playing the Scarab. This was a major downturn in the star’s career, as after numerous scandals, he’d been blacklisted by the major studios. That said, he still is working hard in this, made just two years before his death.
He also has a weapon called the Purple Vibrator, so look out.
This was a very successful serial, but sadly, the strain of playing the physical role was too much for lead Dick Purcell, who died a few months after filming was complete.