The six letters in the word Shazam stood for the six elders who granted Billy their powers: Solomon, Hercules, Atlas, Zeus, Achilles and Mercury.
Jackson Bostwick was fired from "Shazam!" two episodes into Season 2 and replaced with John Davey. Bostwick had sustained an injury during filming, went for medical treatment, and was advised to stay home a few days to recuperate. However, producers mistakenly accused him of holding out for a higher salary. Bostwick successfully sued Filmation, which was forced to pay his full salary for the entire series, including all its reruns on CBS.
Billy Batson's radio work was only mentioned once in the series. A brief line spoken by Billy in the first episode explained that WHIZ had sent him on a roving assignment, to do stories about American youth, with Mr. Mentor as an advisor.
Jackson Bostwick said that when fired from the series, producers explained to him that since this was a kids show, most viewers would not notice another actor replacing him in the role. Bostwick believed that most kids were smart enough to tell a difference, and was largely proved to be correct.
The character Captain Marvel was originally created by Fawcett Comics in the 1940s as a rival to Superman. A successful lawsuit by Superman's owner, DC Comics, resulted in the character disappearing for more than a quarter-century. DC, which had acquired the rights to the character, relaunched him in the comics in 1973. However, during Captain Marvel's long hiatus, DC rival Marvel Comics launched its own, unrelated Captain Marvel character, which prevented DC and the producers of this series from using Captain Marvel as a title. As a result, the title "Shazam!" was introduced (as of 2007, Shazam! is still used on all DC publications featuring the original Captain Marvel). Captain Marvel was actually created in 1939. In mid-1939 an ashcan copy of a comic printed under both the names "Flash Comics #1" and "Thrill Comics #1" was printed purely to secure copyrights for the character, but the names used were already in use elsewhere. The name of the main character was changed to "Captain Marvel", and the title of the magazine changed to "Whiz Comics". Whiz Comics #2, reprinting the stories from the earlier ashcan copy, was printed for distribution in late 1939, and dated February 1940. A copy of the ashcan edition was discovered in 1985, at which time this was considered to be the most valuable comic book in existence.