Black Adam
In the finale of Shazam's origin story, Black Adam holds Billy's foster siblings hostage and demands he give up his power, or they will die. But instead of giving Black Adam his power, he shares it with his foster siblings, empowering them as "Shazams", as well. Together, they fight Black Adam and the "host" that the seven sins have inhabited. Eventually, the collateral damage endangers civilians, so Billy orders them to save the people while he alone battles Black Adam. He finally realizes that his knowledge of his newly acquired powers cannot defeat Adam, who has much more experience using his magic, and decides to change back into his child form. As normal teenager Billy, he challenges Black Adam to also change (into Teth-Adam) to make it a "fair" fight. After some convincing, he does so, but because he has been alive for centuries due only to his "Black Adam form", as a normal human he quickly ages and turns to dust.