Three thousand years ago Teth-Adam was granted the power to be The Champion by the wizard Shazam. In the ancient kingdom of Khandaq Black Adam ruled through strength of arms and protected the world in turn from powers that would threaten its stability. Unlike the current champion Black Adam acts as he does not for the benefit of mankind, or even because he wants to do good. He acts as he does because he’s expected to do so, and in turn expects people to offer him tribute and adulation in return.
Black Adam fights Captain Marvel because he is an usurper. Black Adam sees himself as the true Champion, and nobody can take that title away from him. Even after three thousand years he still possesses all of his might, and Black Adam plans to show the world exactly who is its rightful ruler.