The concept of a multiverse has been around for decades--other versions of our reality that represent the different decisions we could make, and the countless variables of our world. In recent years, though, the multiverse has become a staple of pop culture, whether it's the Academy Award-winning Everything Everywhere All At Once, FX's Devs TV series, or more broadly, the Marvel Cinematic Universe. The MCU kicked open the doors of its own multiverse in 2021 with Spider-Man: No Way Home and began to explore it more deeply with Doctor Strange in the Multiverse of Madness and Ant-Man and the Wasp in Quantumania. Before the MCU ever dared, though, The CW's Arrowverse began exploring the multiverse concept years earlier, predating even Sony's excellent Spider-Man: Into the Spider-Verse.

　　The Flash kicked things off way back in Season 2. One of the biggest mysteries of Season 2 was the question of who was hidden under the iron mask in Hunter Zolomon's cage. The man in the iron mask turned out to be none other than Jay Garrick, the Flash of Earth-2. Series showrunners cast John Wesley Shipp in the role, who was best known for playing The Flash on the CBS TV series, which aired in 1990 and 1991. Alongside Garrick, the show also introduced Tom Cavanagh's second character on the show, Harry Wells, an Earth-2 variant of Harrison Wells. Just weeks later, Barry and Cisco would find themselves on Earth-38, where they would meet Supergirl--a show airing on CBS at that time. That gave us three canonical Earth variants for the CW in 2016.

　　Season 3 then began with Barry's first truly big mistake, when he went back in time to stop Reverse-Flash from killing his mother and, in the process, created a new timeline with lots of changes that gave the Arrowverse showrunners an opportunity to make a lot of little changes. This was the Arrowverse's take on Flashpoint, a comic book storyline that's also being explored in the upcoming Flash movie.

　　DC's Legends of Tomorrow began to explore this space as well. In Season 2 of that series, the heroes came into contact with the Justice Society of America and brought back the first real variant of the Reverse-Flash, played by Matt Letscher instead of Tom Cavanagh. Letscher's take on the character had been previously introduced on The Flash before making the jump to Legends. Once there, he sought out the Spear of Destiny with help from Malcolm Merlyn and Damien Darhk, the latter of whom had died in Arrow Season 4. Together, the three were nearly successful in rewriting reality, and the Legends had to fight a whole army of Reverse-Flash remnants from elsewhere in the timeline.

　　The next big move came with 2017's "Crisis on Earth-X" crossover. This was the second big crossover for the network following the "Invasion" event a year prior, and the first one to use the "Crisis" moniker that DC fans are so familiar with. That crossover took members of Teams Flash, Arrow, and Supergirl, as well as the Legends of Tomorrow, to Earth-X, a version of Earth under rule from fascist versions of the network's primary heroes. Supergirl was Overgirl, and the Green Arrow became Dark Arrow.

　　Everything came to a head in Fall 2019 with the Crisis on Infinite Earths crossover. It's the kind of unprecedented project that we may never see happen on television again, and it felt that way to watch it in real-time. In the ambitious five-part special, we had three versions of Superman played by Tyler Hoechlin (The CW's Superman), Tom Welling (The CW's Smallville), and Brandon Routh (Superman Returns). Grant Gustin's version of Barry Allen came face to face with John Wesley Shipp's version of the same character from that 1990 television show, and for a brief moment met Ezra Miller's big-screen version of the character in a truly shocking cameo. Through other cameos, the crossover established that the 1989 Batman movie, HBO Max's Titans, the 1966 Batman series, the regrettable Birds of Prey television series, and NBC's Lucifer are all part of the same multiverse.

　　The CW's format for these stories is simply a better fit for multiversal exploration. While the network could never go nearly as big as Marvel's multi-billion-dollar franchise can with budgets and scale, a handful of interconnected TV shows allows for more time and space to explore these ideas without waiting years between stories. The size of movies means they inherently have to be big, explosive, and somewhat approachable stories. A television show has anywhere from six-to-20-plus hours to explore these ideas and characters. The Flash can go visit Supergirl for just a single episode. Arrow can bring in an alternate Earth version of Laurel Lance.

　　Neither approach is better, but each does have its own strengths, and the ongoing nature of the Arrowverse let the creatives behind those shows go deeper into the weirdness of multiversal storytelling much more quickly. For all its flaws, the CW got to the multiverse first and did some genuinely creative, weird stuff with it.

　　Eric Frederiksen on Google+