In the late 1940's and early 1950's, Superman was being outsold by C.C. Beck's Captain Marvel line of comics - until DC sued Fawcett for plagiarism and won. Some 20 or so years later, DC obtained the rights to Captain Marvel and co. but by this time, Marvel had produced their own character called Captain Marvel! Hence, the only way this comic could hit the stands was if it was called Shazam! It was - and it ran for 35 issues.