Black Adam is best known as an enemy of Captain Marvel (who is now known as Shazam). However Black Adam has become an anti-hero and has at times fought alongside Shazam. Geoff Johns used Black Adam in Justice Society of America and JSA. Black Adam also had a major role in 52.
Black Adam has powers of Egyptian gods. He is a match for Shazam, who has powers of Greek gods. He is originally from ancient Eygpt and later that is retconned to a fictional middle eastern country. At one point in his long history, Black Adam was shown to be corrupted by his powers or corrupted by a demon. Later it was retconned that he was driven to his more ruthless actions by the conquest of his homeland.
Dwayne Johnson will play Black Adam in the upcoming Shazam movie. It will be his first appearance in a movie. It will be interesting to see Johnson play a character who isn’t quite a full villain or full hero. I am not sure that he has played a part like that.