The Marvel Captain Marvel was created so Marvel would own the copyright on the name, once it was left unclaimed by Fawcett after DC won a suit against them that claimed Fawcett's 1940s Captain Marvel was too much like DC's Superman. Then DC got the rights to that Captain Marvel, but Marvel already had a comic being published under that name so they had to call the comic (and awesome 1970s Saturday morning TV show) Shazam!.
Fortunately I downloaded the complete series of Shazam and Isis before it became traumatic to look for Isis videos online.