Like any character that’s been around awhile, Black Adam has a complicated history. He’s been around longer than most, and that applies both within the DC Universe and in the real world. His history has been rewritten several times, like most characters that date from the Golden Age, but here are some broad strokes with a few notes.
Adam’s first appearance was in 1945, in Fawcett Comic’s Marvel Family #1. Chosen as a champion by the ancient wizard Shazam, Adam gained great power, but instead of defending the people, killed the pharaoh and assumed the throne himself. Shazam banished his former champion to the depths of space. Kept alive by the magic power within him, Adam spent roughly 5,000 years flying back to Earth, arriving shortly after the wizard had chosen a new champion, Billy Batson, who fought crime under the name Captain Marvel. With help from Captain Marvel, Jr, and Mary Marvel, not to mention their non-powered but crafty ally Dudley, Adam was defeated and killed when he lost his power and the millennia of aging caught up with him.
Later, DC Comics bought Fawcett after a lawsuit alleging that Captain Marvel was too similar to Superman (ironically, DC would later lose the trademark to the Captain Marvel name by not using the character often enough, creating decades of confusion about who and what Captain Marvel actually is). In the DC version, Adam was resurrected by Dr. Sivana, a mad scientist who most often clashed with the Marvels. Over the years, and through various reboots of history, Adam slowly evolved from a flat-out villain to something of an anti-hero. Most of his redemption, or at least as much of it as he managed, was in the pages of the Justice Society of America.
After a few more reboots, Adam’s history became linked with the country of Khandaq, one of DC’s fictional places in the Middle East. It was also amid these reboots that they added the new detail that, in ancient Egypt, Teth-Adam, as he was known then, served Prince Khufu, who would go on to become the reincarnating hero Hawkman. Adam, in this newest history, ruled Khandaq, had a wife and son that he lost, and that led to his dark turn. In various tellings, his family were completely mortal, or powered themselves. In the modern versions, his wife was Isis, a new character loosely based on one from a Saturday morning live-action tv show, and his son was Osiris. Interestingly, Isis’ real name is given as Adriana Tomaz, which is one of the roles listed in the upcoming movie.
At present in the DCU, Black Adam is ruler of Khandaq, neither hero nor villain, simply the leader and defender of his people. He is far more ruthless and brutal than most of the heroes, but dedicated to his country, setting him apart from most of the villains. His regal bearing, arrogance, powers, and general appearance (dark hair and pointed ears in most depictions) have often led to comparison with another ruler that tends to alienate those around him: Marvel Comics’ Sub-Mariner.
Originally simply an evil opposite of the hero Captain Marvel (the original one), Adam’s powers were later fleshed out and made a bit more distinct. He has the stamina of Shu, the swiftness of Horus, the strength of Amon, the wisdom of Zehuti, the power of Aten, and the courage of Mehen, making him a fitting counterpart for Captain Marvel’s abilities. Over time, all the characters powered by the wizard Shazam have had their powers change slightly. Originally, the magic lighting transformed them from mortal to vastly powerful superhumans; now, they can use the lightning itself as a weapon of great power. Adam’s physical abilities place him on par with Superman, but without that great hero’s morals.
In addition to the comics where he was created, Adam has appeared in many different cartoons and video games. The upcoming movie will be the first time he has been depicted in live action. How he will fit into the somewhat inconsistent DCEU remains to be seen.