The Kingdom Come version of Superman is coming to Crisis on Infinite Earths, but who is this particular version of the Man of Steel? At San Diego Comic-Con, it was announced that Brandon Routh, who played the title role in 2006's Superman Returns, will portray the Kryptonian hero once more in this year's Arrowverse crossover. What's more, at the panel for Arrow, Routh opened his shirt to reveal the distinctive black and red "S" shield of the Superman from Kingdom Come.

Routh returning to play Superman is exciting for a few reasons. While Superman Returns underperformed at the box office and didn't win fans over, Routh's steadfast portrayal of the Man of Steel was the film's bright spot. The actor was understandably disappointed when Warner Bros. didn't pursue sequels, which Routh was signed for, and opted instead to wait seven years before rebooting Superman in Zack Snyder's Man of Steel with Henry Cavill in the title role. But Routh found success as a different superhero; he took the role of the lovably earnest Ray Palmer/The Atom in Arrow before becoming one of the headliners of its spinoff, DC's Legends of Tomorrow. For Crisis on Infinite Earths, Routh will play both Palmer and Superman, who comes from an alternate Earth in DC's Multiverse. Even better, Supergirl's Superman, played by Tyler Hoechlin, will also play a role in Crisis - so fans will get to see two different versions of the Man of Steel meet on-screen for the first time.

Related: The Arrowverse Teased Brandon Routh As Superman Three Years Ago

When Routh's comeback as Superman made news, fans naturally assumed he would portray the same character he played in Superman Returns. But, in typical Arrowverse fashion, the producers threw an unexpected curveball by introducing Routh as the Kingdom Come Superman. Here's who and what exactly the Kingdom Come Superman is, and what it could mean for Crisis on Infinite Earths.

Kingdom Come Explained

Kingdom Come art by Alex Ross

Kingdom Come was an immensely popular 4-issue limited series published by DC Comics under their Elseworlds label in 1996. Written by Mark Waid, who showcased his deep love and expertise of DC Comics lore, and painted in a breathtakingly photorealistic manner by Alex Ross, Kingdom Come was the story of a possible apocalyptic future for the DC Universe. Ross was coming off his groundbreaking Marvels, which told of the origins of the Marvel Universe from the point-of-view of photographer Phil Sheldon. For Kingdom Come, Waid and Ross used a minister named Norman McCay as the POV character, a normal man who received apocalyptic visions of the cataclysm ignited by DC's superheroes.

In Kingdom Come's future, Superman abandoned his role as protector of humanity after the Joker killed Lois Lane (a plot point that would later be borrowed by the Injustice video games and comics). Without the Man of Steel to serve as a guiding light of morality, a new generation of superheroes (many the children of the Justice League) grew up inspired by Magog, a more brutal type of hero who was meant to embody the 'grim and gritty' comic book superheroes of the 1990s. Magog and his super friends caused the Parasite to explode, irradiating much of the American Midwest (including Superman's boyhood home state of Kansas). Wonder Woman coaxes Superman to return to the world and he does so with a mission to bring all superheroes to heel. Superman reassembles the old Justice League, renamed the Justice Battalion, and begins imprisoning metahumans who refuse to conform to his ideals in a gulag.

Rising up against Superman's 'fascist' ways are Batman, who has gathered his own team of underground, outsider heroes, and Lex Luthor, who masterminds a group of supervillains billing themselves as the Mankind Liberation Front. Luthor's Superman-killing ace-in-the-hole is a mind-controlled Captain Marvel (before he was officially renamed Shazam by DC). Eventually, the superhuman conflict comes to a head when the gulag is broken open, which ignites an all-out war. The United Nations orders nuclear warheads deployed to kill all of the metahumans but Captain Marvel, who breaks free of Luthor's mind control, sacrifices his life to destroy the nukes, although the resulting detonation kills most of the metahumans. Superman survived, however, and he chooses to work with the UN so that the remaining superheroes integrate with and inspire the communities they're meant to protect.

Related: Alex Ross Imagines Brandon Routh As Kingdom Come Superman

Kingdom Come is one of the seminal DC Comics stories of the modern age. It inspired a sequel called The Kingdom, which was far less successful because Alex Ross wasn't involved. The Kingdom Come characters, specifically Superman and Magog, also made appearances in the mainline DC Universe and the Kingdom Come world was made part of the DC Multiverse, designated as Earth-22.

Kingdom Come Superman Explained

Superman Kingdom Come

The Kingdom Come Superman is an unforgettable version of the Man of Steel and he understandably captured fans' imaginations. Portrayed as noticeably older, with his hair greying at the temples, the grim and stoic future Man of Steel was a commanding (and intimidating) presence. Fans were also struck by the altered "S" shield on his chest, which changed the yellow background to black; the T-shirts DC made of the Kingdom Come "S" were best-sellers. Most compellingly, the Kingdom Come Superman wasn't the bright, optimistic boy scout fans were accustomed to; he was both a response to and a reflection of the violent comics of the 1990s.

Kingdom Come Superman was defined by his sadness and the loss of his innocence; after Lois died and Magog killed the Joker in response, Superman retreated to the Fortress of Solitude for a decade and pretended to be a farmer in a holographic simulation of Smallville. This version of Superman lost his faith in humanity and abandoned the world; when he returned to set the world right, he did so with strongarm tactics and intimidated other superheroes to fall in line behind him. However, unlike the Injustice version of Superman, Kingdom Come Superman's heart was still in the right place and he eventually came to see the error of his methodology. Kingdom Come's epilogue saw Superman reconcile with Batman and start a romance with Wonder Woman, which would lead to them becoming parents.

How Kingdom Come Superman Fits Into Crisis On Infinite Earths

Since Crisis on Infinite Earths is a story about entire worlds across the Multiverse being destroyed by the Anti-Monitor, it makes sense for Kingdom Come Superman to join the Arrowverse. Just like how the Flash (John Wesley Shipp) from the 1990 CBS TV series played a role in Elseworlds to save his world from the Crisis (and thus joined the Arrowverse's canon), it's a prime opportunity to introduce the Kingdom Come universe into the Arrowverse as well. It's unclear whether Routh's Kingdom Come Superman will resemble the older, grey-haired version of the comics but, given the Arrowverse's dedication to being comics-accurate, it's highly likely Routh's Kingdom Come Man of Steel will wear a version of the comic book costume complete with the red and black "S" emblem.

Related: How There Can Be Two Actors Playing Superman In The Arrowverse

Routh expressed mixed feelings about donning Superman's cape once more but he saw it as a chance to give closure to the role that the actor never got to see through to its full potential. Indeed, when Routh's return as Superman was announced, fans automatically assumed he would be continuing the character he portrayed in 2006. Further, the Superman Returns Man of Steel is the same character played by Christopher Reeve and director Bryan Singer's film was a sequel to Superman II; this would have meant that the Reeve films would join the Arrowverse's canon as well. However, Routh's Kingdom Come Superman likely means he's playing a different version of the character in the Crisis- unless the Arrowverse cleverly fuses both Supermen together.

It could turn out that Routh is still playing the same Superman from Superman Returns but the continuity of the Reeve/Routh movies evolved into the Kingdom Come universe off-screen. After all, much like the Kingdom Come version, Routh's Superman also abandoned the world for a number of years and he was a sadder and more alienated version of the character than the Superman Tyler Hoechlin plays on Supergirl. By the end of Superman Returns, Lois remained with her fiance Richard White (James Marsden) and they were raising Jason (Tristan Lake Leabu), who was actually Superman's son. Since it's possible that the Reeve and Routh films are set in the past, possibly decades ago, it could easily mean Routh's Superman is indeed older than Hoechlin's and could have turned into the Kingdom Come Superman.

While this fusion of continuities could fit, it remains to be seen if the Arrowverse will pursue this angle, since already having two Superman together on-screen could be complicated enough. It's just as likely Routh will play Kingdom Come Superman as a different version of the character in Crisis on Infinite Earths that only spiritually draws from and evokes his performance in Superman Returns. Either way, Superman will be fighting to preserve his world in the Crisis and Brandon Routh playing the older and grimmer Kingdom Come Superman will be a fascinating contrast to both his prior portrayal and the hilarious gee-whiz optimism of Ray Palmer.

Next: The Arrowverse's Crisis On Infinite Earths Explained