Alexander Luthor Sr. originally came from Earth-3, the opposite universe to Earth-1. He was inspired by Lois Lane to fight the Crime Syndicate of America and become his earth's first and only superhero. He eventually married Lois and they later had a son named Alex. In Crisis on Infinite Earths Alexander sees his universe being destroyed and in a last ditch effort to save his son, he sends him to another universe to be safe. He then dies with his wife Lois when the Earth-3 universe is destroyed, making his son the only survivor of his universe.
Not only was Alexander the " Superman" of his universe but just like Jor-El (Superman's Father) he sends his son away in a ship to save him. Thus making his son the only survivor of his world. An obvious parallel to the Superman origin story.
Alexander Luthor made his reappearance post-Crisis as an inhabitant of the anti-matter earth, this time using an armor more close to the one used by his positive matter doppelganger. More arrogant but still heroic as his previous incarnation, Alexander traveled through the matter-antimatter membrane to recruit the JLA in depose the evil CSA of the control of his world. However, later he discovered than everything was orchestrated by Brainiac, who wanted destroy both worlds. Also, because of the nature of his anti-matter universe, his efforts were doomed to failure.
New 52/Forever Evil
During the Forever Evil event, Alexander Luthor makes his appearance as a captive of the Crime Syndicate that have invaded the prime Earth. He is ultimately freed by Captain Cold and Black Manta, where he utters the phrase "MAZAHS!", to become a doppelganger to Shazam. Alexander then proceeds to kill Johnny Quick and steal his speed powers. He then declares he will kill the Crime Syndicate and become the greatest hero of the Earth he has been brought to.
It is then revealed that Ultraman and Superwoman have been collaborating together and the baby that she has been carrying is neither Ultraman's or Owlman's, it is actually the child of Alexander (this character is most likely the New 52 version of Alexander Luthor Jr.). Ultraman and Alexander proceed to fight with Ultraman declaring that he is more powerful and he has defeated Alexander before and he will do it again. Alexander retorts that since he has absorbed the powers of many fallen Crime Syndicate members, he is the one that is more powerful. He proceeds to knock out Ultraman and kill Deathstorm. Alexander then sets his eyes on Lex Luthor and his team. He appears to overpower all of them including an attempt by Sinestro and Black Adam to revert him back to his normal form by letting Black Adam shout Shazam, this attempt is unsuccessful and Alexander even manages to kill Bizarro. This enrages and even appears to sadden Lex Luthor who claims that although Bizarro was merely monster, he was his monster. Lex had previously looked into Alexander's eyes and had realized that he and Alexander are the same person. Although Alexander taunts Lex by stating that this world contains version of themselves that are all weaker, Lex shouts out Mazahs and reverts Alexander back to his normal form. This gives Lex time to stab Alexander and thus killing him with Lex telling him that even though he is not as strong or powerful, he is smarter than Alexander. Ultraman returns and congrats Lex on defeating Alexander but the Justice League's are then freed from the prison at that moment and the moon is pushed out of the way of the sun, thus removing Ultraman's powers. Lex claims victory over Ultraman and gloats that he will not kill Ultraman as he is more happy to see him in such a weak state.
In the Pre-New 52 universe, Alexander Luthor Sr. was not unlike his counterpart Lex Luthor in that he did not have any superhuman abilities or powers and relied on his great intellect to create gadgets, armor, and weapons to combat the Crime Syndicate.
In the New 52, Alexander Luthor's powers are changed dramatically as he is given powers similar to that of Shazam. To revert to his powerful form he shouts out the word Mazahs (a reverse spelling of Shazam). Alexander also appears to have the ability to steal the powers of other super humans, and he does this to Johnny Quick and steals his super-speed before killing him. Alexander also states that he has stolen powers from other Crime Syndicate members such as Hawkwing and Will Baston (possible Earth-3 versions of Hawkman and Billy Batson/Shazam)
Justice League: Crisis on Two Earths
Alexander Luthor is a central character of the 2010 animated film Crisis On Two Earths, voiced by Chris Noth. In a story very close to the 2000s JLA: Earth2, Alexander is the last surviving member and leader of his world's heroic team, who have all been killed by the Crime Syndicate. As a last desperate resource, he travels to an alternate reality to recruit the assistance of the Justice League. Originally, this history would be an extended episode of the Justice League Animated series and would fill the gap between the JL first series and the Unlimited era.