[CMIII]

Technically his name isn't Shazam! it's Captain Marvel which dates back to 1940 in 1950 when DC "got" the rights they yet again did not secure them. In the 1960's Marvel Comics created a character Named Captain Marvel (Mar-Vell) and conditionally secured the rights (they must use the name every year). When DC decided to bring Captain back Marvel had secured the name they needed a new title it Became SHAZAM!. Most of the rest is legal stuff the Boxes for both Mary and Freddy call him shazam and call them by their unpowerd names Mary Batson and Freddy Freeman (Mary Marvel and Captain Marvel Jr).

It is fairly stupid most fans of the character call him Captain Marvel and even prior to the N52 the other characters and most DC staff did as well