This was the first depiction of a comic book superhero on film.
Superman was originally considered for this project, however, when National Periodical Publications (now known as DC Comics) turned Republic down, the producers made the offer to Fawcett Comics for its top character and was accepted.
Billy Batson becomes Captain Marvel by speaking the name of the wizard Shazam: S = The Wisdom of Solomon; H = The Strength of Hercules; A = The Stamina of Atlas; Z = The Power of Zeus; A = The Courage of Achilles; M = The Speed of Mercury.
The film was released in 1941 and depicts Americans freely entering and exiting Siam (Thailand). This would become impossible later that same year. On 21 December Siam signed a formal military alliance with the Empire of Japan. On 25 January 1942, Siam formally declared war on the US, because Japan and the US were already in a state of war.
Captain Marvel's costume, which is red in comic books, was actually blue/gray in order to photograph better in black and white.