Black Adam (New 52)'s History
Teth-Adam was a slave in Kahndaq, where almost the entirety of his family was killed by the dictators — all except his nephew Aman, whom Adam eventually managed to contact and help escape from imprisonment, being mortally wounded by guards in order to buy him time.
Aman, however, refused to abandon his dying uncle, and rescued him. Together, while escaping the underground prisons, they found themselves magically transported into the Rock of Eternity, where they were greeted by Shazam. The wizard, deeming Aman pure, offered him the role of his champion, giving him the task of freeing Kahndaq — which Aman accepted on the condition that Shazam healed Adam. Explaining that the gift bestowed upon him could be shared with his family, Shazam gave Aman his powers, healing and empowering Adam in the process.
Being returned to Kahndaq, Aman and Adam contemplated how to use their powers in order to free their people. While Adam was willing to destroy the dictators and exact revenge for their dead family, Aman wanted to save them and give them peace, stopping all bloodshed. Fearing that Aman's method would not work, Adam killed him and seized his powers for himself, seeing it as a necessary sacrifice for the greater good.
Black Adam is known in legend for having defeated the dictators and the Seven Sins, successfully freeing Kahndaq. Though myth says he merely disappeared, Black Adam actually turned against the Council of Eternity and murdered all its members but Shazam — the wizard, however, managed to overpower and seal Black Adam away.