Warning: Contains SPOILERS for Crisis on Infinite Earths Part 3.

Crisis on Infinite Earths implied that Lex Luthor somehow doesn't know that the Arrowverse's Superman and Clark Kent are one and the same — but the reveal actually makes perfect sense. Created by Jerry Siegel and Joe Shuster, Lex Luthor made his comic book debut on the pages of Action Comics #23. The Arrowverse's incarnation of Luthor made his debut in Supergirl season 4. Played by Jon Cryer, Lex served as the primary antagonist before he was killed by his sister, Lena Luthor.

Ahead of the Crisis on Infinite Earths crossover event, however, Lex Luthor was resurrected by the Monitor. Much to the chagrin of Supergirl, Luthor has since spent Crisis on Infinite Earths alternating between helping the heroes and characteristically betraying them. One of his latter efforts saw him abscond with the Book of Destiny, which he used to jump between surviving universes to kill every version of Superman he could find. That quest ultimately led him to Tom Welling's Clark Kent from Smallville. That Clark Kent was Superman on Earth-167 seemed to surprise Luthor. "Where I come from that would be ridiculous," he said. "He can't see past his glasses."

Related: Crisis On Infinite Earths: Original Superman Movies ARE Arrowverse Canon

The implication had many questioning how this version of Lex Luthor doesn't know that his Superman is also Clark Kent, especially since he deduced that Kara Danvers is Supergirl. The answer, however, actually lies in the source material. In Man of Steel #2, the villain tried to figure out Superman's identity with the assistance of several detectives and even a supercomputer. The results ultimately revealed that Superman was Clark Kent. Luthor, however, dismissed the revelation as erroneous because he was unable to comprehend that beneath the God-like powers, Superman could be somebody so ordinary. As such, it's not a stretch that the Arrowverse's Lex Luthor would be similarly arrogant and able to dismiss the truth even as it stares him in the face.

Lex Luthor in Crisis on Infinite Earths Part 3

Luthor's hubris was further reflected in his interaction with Welling's Clark Kent. Learning that Kent had given up his powers, Luthor became incredulous. After all, Superman is as close to an equal as Luthor would ever admit to having. As such, not only is Luthor mentally unable to comprehend that Superman could be ordinary, he especially cannot fathom why Superman would actively choose to be. Given that he didn't address the encounter in Crisis on Infinite Earths Part 3, it's plausible Luthor's chosen to dismiss the possibility of his Kent being Superman.

Much like The Joker and Batman, both Superman and Lex Luthor are somewhat defined in relation to each other. There's a reason Luthor breached between Earths rather than first target his Superman, whom he knew to already be on the Waverider. As much as Luthor wants to kill Superman, there will always be a part of him that fears succeeding.

Of course, fans' ability to suspend their disbelief will no doubt be stretched to its limits after this encounter. In Crisis on Infinite Earths Part 2 alone, Luthor knew that Earth-38's Kent was traveling the multiverse with Lois and Iris, only for Earth-38 Superman to be there, instead; yet, Luthor still did not make the connection. But, if every character always acted in the exact same manner as the show's viewers, there would be no room for surprise. Besides, with still two parts of Crisis on Infinite Earths remaining, and Luthor having usurped "Kingdom Come" Superman's position as the Paragon of Truth, there's a chance that the Arrowverse may yet have Luthor finally accept the Superman in the room.

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