Alexander Luthor, Sr. was born on Earth-Three. Finding solace in deep scientific research and invention, Alexander created many notable and advanced devices which brought him public notice. But it was not until his native world became the target of his extra-dimensional counterparts, the Luthors of Earth-One and Earth-Two that he decided to openly fight as a champion for his world. Realizing that he could not win the day alone against such odds, He recruited the help of his counterparts' greatest enemies, the Supermen of Earth-One and Earth-Two.
After bringing the Supermen to Earth-Three, Alexander enlisted their aid to directly confront his villainous counterparts, who planed to use his world as a base from which to destroy their own home worlds. They had recruited Ultraman to act as the muscle in their scheme. Since he was powered by kryptonite, he was easily able to overpower his extra-dimensional counterparts. This spurred Alexander to don a suit of powered armor and confronted Ultraman. Using his advanced weaponry, he was able to defeat Ultraman by temporarily "de-phasing" him. This allowed the two Supermen to recover and defeat the already squabbling Alexei and Lex Luthor.
With Alexei and Lex defeated, Alexander returned the two Supermen to their native dimensions and Ultraman to his prison. Inspired by the encounter, he decided on to remain an active and open heroic presence to his world. He later married Lois Lane and fathered a son with her.
Over the intervening years Alexander would face and defeat Ultraman and the Crime Syndicate many times. This continued up until the Anti-Monitor's energy wave appeared and started to sweep through the Earth-Three universe. To halt the wave, he was forced to join forces with his enemies. Despite their combined power, they were unable to stop the advancing wall of anti-matter.
Alexander and his wife were only able to save their son from the complete destruction of their reality by placing him in a capsule which would take him to Earth-One. Alexander, along with everyone else native to his universe, died in the Anti-Monitor's attack. The existence of Alexander Luthor, Earth-Three, and all of its denizens was ultimately erased from all history, save for in the memory of Alexander Luthor, Jr.
- Genius Level Intellect: Alexander Luthor, Sr. was a brilliant inventor responsible for creating various highly advanced scientific devices for the benefit of his world.
- Super Suit: Alexander Luthor, Sr. wore a specially designed super-suit and matching helmet, which enabled him to fly as well as project energy blasts and turn intangible to himself and others.
- Super Weaponry: Alexander Luthor, Sr. employed a wide variety of advanced weaponry of his own design. Nearly all of these items however have never been openly revealed.
- Alexander Luthor, Sr. is also known as Luthor of Earth-Three and Luthor III.
- 8 Appearances of Alexander Luthor, Sr. (Earth-Three)
- 8 Images featuring Alexander Luthor, Sr. (Earth-Three)
- Quotations by or about Alexander Luthor, Sr. (Earth-Three)
- Character Gallery: Alexander Luthor, Sr. (Earth-Three)