“The character was originally created in 1940 for the long-defunct publisher Fawcett Comics, who ceased publication of their Captain Marvel in the early 50s under legal pressure from DC Comics, who claimed the character infringed on Superman. In 1967, while that Captain Marvel was still in publishing limbo, Marvel Comics created their own character with the name of “Captain Marvel,” and trademarked it. So when DC eventually gained the rights to publish former rival Fawcett’s Captain Marvel, they couldn’t call him that on the covers of any books featuring him.”
– DC’s Captain Marvel Officially Changing His Name to the Non-Trademark Infringing ‘Shazam’