On Earth-3, the Crime Syndicate have taken over all of America and presumably the world. With nearly all who resist being killed instantly, Alexander Luthor was the only one left who could stand up to them.
Initially portrayed as a hero, Alexander Luthor was later rebooted into an even more villainous version of Lex Luthor during the Forever Evil miniseries. This change in character was to contrast Lex Luthor's own character development from villain to hero. Alexander Luthor believes himself to be the world's greatest superhero and as such has no qualms killing anyone he deems evil.
At some point, he had an affair with Superwoman. They conceived a child that is implied to be the Earth-3 equivalent of the First Born from Wonder Woman
Eventually, Alexander Luthor was captured by the Crime Syndicate and held prisoner. Their reason for keeping him alive being that they may need his mind for the looming threat that appeared in their universe. They make their way to the Prime Earth, incapacitate the Justice League and wreak havoc on America. All the while, Alexander is bound and gagged. When Captain Cold and Black Manta find him, they remove the tape from his mouth, causing him to cry out "MAZAHS!" and change into a Shazam-like superhuman. Alexander then goes around killing any superhumans he can find so he can absorb their powers. After killing Bizarro, Lex Luthor decides to put an end to his counterpart by sticking a lightning rod in his chest and crying out "MAZAHS!", knowing that by aving the same voice he would be able to use the same powers as Alexander. The plan works and Alexander Luthor loses his powers. In order to stop him from changing again, Lex muffles Alexander before stabbing him through the heart.
Powers and Abilities
Just like Lex Luthor, Alexander Luthor is one of the smartest men of his time.
Power Absorption and Mimicry
Alexander has the ability to absorb the powers of anyone he kills. When he first appears in Forever Evil, he'd already acquired the power of MAZAHS from William Batson, hence his Shazam-like appearance.