The CW's superhero shows have been cross-pollinating since the second season of Arrow, when Barry Allen, aka the Flash, was introduced on the series. The following year, Arrow and the new Flash series had their first official crossover, kicking off a yearly tradition. Next came the arrival of Vandal Savage, requiring the combined efforts of Green Arrow, Flash, Hawkman, Hawkgirl and more to stop him. And things were pushed even further last year when the Dominators' invasion of Earth was thwarted by everyone, from Team Flash and Arrow to the Legends of Tomorrow and, perhaps most notably, Supergirl -- a character who actually resides in a different dimension from the rest of the weekly Arrowverse shows.
This year, the team of superheroes will come together once again to battle a major force of evil in "Crisis on Earth-X". Set pictures of the currently-filming crossover have surfaced online, and with them came our first looks at the villains of the ambitious event. In addition to our first glimpse of Prometheus-X, who will be facing off against Stephen Amell's Green Arrow, pictures of the masked, red-and-black clad Overgirl quickly have arrives. And while some fans on social media seemed shocked at the idea that there could be a twisted, nazified version of Supergirl, like just about everything else in these shows, the character originated in the comic books.
In the comic books, just like in the Arrowverse, Earth-X (pronounced "Earth Ten") is an alternate universe where the nazis, not the Allies, won World War II. This means that this world's reality and history is much different than the one we know, where most every superhero we are familiar with is a twisted nazi version of themselves. This isn't your favorite superheroes who have turned evil, like Marvel's evil Hydra-influenced Captain America seen in Secret Empire. For the most part, they're not the same characters, but rather evil, distorted doppelgängers.
Thus, Overgirl is not Melissa Benoist's Kara Zor-El turned nazi -- she's another character altogether.
Overgirl has similar powers to her cousin, Overman, the evil version of Superman, Kal-L (not "El"). On this Earth, Kal's origin involves his rocket crashing on the planet after the destruction of Krypton, but instead of being raised by homegrown, all-American Kansas farmers, he was raised by nazis to become a soldier in their cause. These Nazis would in turn use the alien's genetic materials to create Overgirl. While the two superpowered beings are not technically related, this nonetheless prompted Overman to view Overgirl as a cousin of sorts.
Overgirl hasn't been featured in many comic book stories, but her existence is still a noteworthy one. She "fell" from her universe and crashed in the DCU in Grant Morrison's 2008 Final Crisis, closely followed by Overman who was searching for her. She also briefly appeared in The Multiversity - The Mastermen #1, another comic written by Morrison. This story, set entirely on Earth-10, told in detail the tale of Kal-L, from his arrival on a nazi-controlled Earth to his position as leader of a nazi-fied version of the Justice League. In many ways, this comic book could be seen as the main inspiration for "Crisis on Earth-X".
Alternate Earths are the norm in the DC Universe, and they've presented as such on The Flash as well. As the Arrowverse heads into its next big crossover, The CW's DCTV shows continue to look to the comic books as inspiration, taking our favorite heroes on an adventure they've never seen before. In "Crisis on Earth-X," Green Arrow, Flash and Supergirl will find themselves in a world much different from the ones they know, where they'll have to battle mirror versions of themselves -- only this time, they'll be punching nazis in the face at the same time.