Well, the answer to that was in Shazam's past, as he tried to create a champion before Billy, in ancient Egypt, having Teth-Adam say his name, to become the Mighty Adam, later to be known as.....Black Adam!
Here's his story!
The Mighty Marvels Join Forces
Shazam relates the story of Black Adam to the Marvel Family (Captain Marvel, Mary Marvel, Captain Marvel Jr. and Uncle Marvel), telling of Shazam's younger days, when he tried to pass his powers on to Teth-Adam, who after saying the wizard's name, became the Mighty Adam....except that the adult Teth then used the wizard's powers against the people of Egypt.....so Shazam banished him to the farthest star....and he had just returned to face the wizard and the family in this issue!
This story had been reprinted a few times by DC Comics (in Shazam! #8 and in Shazam! From the Forties to the Seventies), as well as being included in a villain pin-up in Limited Collectors' Edition #C-39, so, one could tell E. Nelson Bridwell had plans for Black Adam!
The World's Mightiest Villain Returns
Dr. Sivana is the reason for Black Adam's return, having invented a resurrection machine, the world's wickedest scientist revived Teth-Adam, who said the wizard's name and became Black Adam again!
Black Adam went out to menace Billy Batson and his Uncle Dudley (who had been traveling the country in an RV), with Black Adam and Captain Marvel being equally matched again, but, Uncle Dudley used the same trickery to get Black Adam to say the wizard's name again, allowing Captain Marvel to defeat the villain (though with less fatal results this time).
When Earth's CollideDC had been hinting at.
Immortal wizard Karmang wanted to revive the ghosts of his Mars, and figured the only way to do that was by smashing Earth-1 and Earth-S together to release enough energy to do that. Using Black Adam and the sand creature from Quarrm to manipulate Superman and Captain Marvel into battle, Karmang almost succeeded, if not for the help of Supergirl and Mary Marvel. One of the most notable events of this issue was Cap's use of the magic lightning as a weapon against Superman, but the story really only used Black Adam as one of two power beings to manipulate the heroes, sadly a trend that would continue in his early appearances.
World's Finest Comics and the Monster Society
This time around, Black Adam had found himself on Earth-1 after his defeat at the Rock of Eternity (with Superman unknowingly freeing him from the Egyptian tomb he had been trapped under), and he planned on taking over that world...
....if not for some help from Captain Marvel and the powerless Billy Batson of Earth-1, who used a variation of the trick Uncle Marvel/Dudley used to defeat Black Adam yet again. But, whether that Billy ever got to become a Captain Marvel on his own was a point that would soon be rendered moot....
one brief new beginning, Black Adam returned again, to face Captain Marvel, then later the heroes of the Freedom Fighters and the Justice Society of America as well as Captain Marvel and his family....even getting a six issue mini-series of his own! Well.....Shazam! to you, Black Adam, and thank for being part of over 75 years of Shazam! history.