The first villain Shazam defeated was Black Adam. Black Adam sought to use his powers for his own gain and so Shazam banished him to the farthest star in the universe.
Black Adam returns 5,000 years later and seeks to get his revenge on Shazam. The Marvel Family defeats Black Adam in the pages of Marvel Family comics #1 (published November 21, 1945)!
The second villain defeated by Shazam was the Mad Mummy! The Mad Mummy appears in Marvel Family comics #79 (published November 21, 1952). In the pages of this comic we discover that the Mad Mummy had once been the ruler of the netherworld and had sought to take over the world of the living. The Mad Mummy was defeated by Shazam's white magic.
Shazam had buried the Mad Mummy and his evil pyramid under the sea, but it was discovered and opened by archeologists and the Mad Mummy was on the loose again. It took the combined efforts of the Marvel Family to defeat him and once again send him to the bottom of the ocean!