While the character was, at one time, the most popular character in all of comics, Captain Marvel was the subject of lawsuits from the beginning, as the company that would become DC sued creator Fawcett Comics claiming that Captain Marvel infringed on their copyright of Superman.
Eventually, DC would actually license the character themselves, but since Marvel Comics had created their own Captain Marvel in the interim, DC could not use that name as the company would then find itself on the receiving end of another lawsuit.
DC’s Captain Marvel comics began way back in 1939 and when young boy Billy Batson said the word “Shazam” he transformed into the superhero Captain Marvel.
Fawcett would eventually settle out of court and cease production of Captain Marvel comics.