All-Star Superman, by Grant Morrison and Frank Quitely, is a timeless classic, embodying the perfect Superman tale. This rich and nuanced 2006 maxi-series is layered with hidden meanings and references to the Superman lore.

However, one mysterious point of the story still stands, and it has to do with the true identity of Dr. Leo Quintum.

Introduced within All-Star Superman, Leo Quintum is an eccentric billionaire genius. This scientist is the head of P.R.O.J.E.C.T., a think tank that was inspired by Superman to create the world of tomorrow. Through breakthroughs in genetic engineering and universal exploration, Quintum worked to shape humanity in Superman's image. At the beginning of the series, Quintum's voyage to the sun is attacked by Lex Luthor and saved by Superman.

This rescue overloads Superman's cells with solar energy, slowly killing him. Even so, Quintum dedicates himself to either saving Superman or replacing him so humanity will not be left behind. As proof, Quintum introduces the Man of Tomorrow to all of his genetic breakthroughs, including photosynthetic giants, Bizarro worker drones, voyager titans and nanonauts.

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Quintum and his scientists even delve into the dangerous Bizzaro-verse, an underworld of sorts. Enlisting Superman's help, Quintum is able to cut the Earth off from the deadly pull of the Bizarro-verse. During the Man of Steel's final days, Quintum impressively finds a way to re-enlarge the Bottle City of Kandor. Moreover, Quintum manages to move the Kryptonians on Kandor to Mars, where they will have more room to live and enjoy Superman's powers.

Most importantly, Superman entrusts Quintum with his genetic code, enabling the scientist to reproduce his own Supermen. In the final pages of All-Star Superman, it seems that Quintum intends to use this information, ensuring that humanity is taken care of in Superman's absence.

Given everything that Quintum accomplishes throughout All-Star Superman, he's clearly a benevolent genius. Yet many have theorized that Leo Quintum, in reality, is none other than the malicious Lex Luthor, turning over a new leaf. This theory is based on a moment near the end of the series when Luthor gains Superman's powers. Lex sees through Superman's eyes, in a moment of illumination. Many believe that, from here, Luthor traveled back in time to become Leo Quintum and aid Superman's endeavors.

One common trait between Luthor and Quintum which makes this theory plausible is their strong determination. For example, when Luthor attacks Quintum's voyage to the sun, Quintum is resolved to finish his mission for the good of mankind. Similarly, Luthor is determined to destroy Superman once and for all, despite being sentenced to death. The main difference here is Luthor's hatred of the Man of Tomorrow being the core of his goals instead of concern for the future.

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In a famous line, Superman says that Luthor "could've saved the world years ago," indicating how his vendetta held Lex back from achieving anything significant. Quintum, on the other hand, has all of Luthor's genius, yet no hatred for Superman. Quite the contrary, Quintum works with the Man of Steel to create a better world, possibly using his genius as Lex to finally save humanity instead of building another weapon. This clear difference likely came about when Lex gained Superman's powers, finally seeing the Man of Tomorrow's hopeful perspective.

Of course, it's also likely that Quintum is simply another genius billionaire with no relation to Luthor. Quintum could just represent everything that Luthor might have been. Still, given the fantastical nature of All-Star Superman, Luthor becoming Quintum is not entirely far-fetched. While it remains a mystery as to whether Lex Luthor is Leo Quintum or not, the fact that they can be compared in the slightest is a testament to Superman's impact on humanity.

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