Marvel's What If...? series is going to feature the voices of a lot of original Marvel Cinematic Universe cast members. Marvel Studios boss Kevin Feige announced the show back at Comic-Con last month and explained that it would be unlike anything we've seen thus far.

He appeared at the D23 Expo to say the same thing while introducing Hayley Atwell to the enthusiastic crowd. Atwell is reprising her role as Peggy Carter in an episode where she takes the Super Soldier Serum instead of Steve Rogers.

If that wasn't enough Hayley Atwell and Kevin Feige introduced some footage from the upcoming Marvel's What If...? animated series, featuring Peggy Carter in a British Captain America-type of suit. Some of the actors returning to lend their voices to the new series are Josh Brolin, Michael B. Jordan, Michael Douglas, Mark Ruffalo, Sebastian Stan, Tom Hiddleston, Samuel L. Jackson, Chris Hemsworth, Chadwick Boseman, Paul Rudd, Jeremy Renner, Karen Gillan, Natalie Portman, Taika Waititi, Stanley Tucci, Neal McDonough, Sean Gunn, Dominic Cooper, David Dastmalchian, Michael Rooker, Jeff Goldblum, and more. This is a pretty impressive cast and leads to a lot of speculation about what types of stories will be told.

Related: Peggy Carter Becomes a Super Soldier in First Episode of Marvel's What If

Marvel's What If...? is based on the comics of the same name and speculates what would happen in popular moments in Marvel's history had they gone in a totally different way. Like the comics, which were introduced in 1977, the Disney animated series will introduce us to Uatu the Watcher, played by Jeffrey Wright (Westworld), who is a celestial being watching over the events of the Marvel Universe as they unfold without taking part himself. The Watchers were first shown in the MCU during Stan Lee's Guardians of the Galaxy Vol. 2 cameo.

Jeffrey Wright's Uatu will serve as the narrator in Marvel's What If...? series, which is going to turn the MCU on its head. It honestly just sounds like a good time for all involved and one can imagine it was easy to convince the stellar voice cast to come back a reprise their roles. The show is expected to premiere in 2021, which will be during the end of the MCU's Phase 4, which is shaping up to be pretty wild and different from Phase 3, which was, for the most part, a pretty serious affair, save for some of Marvel's trademark humor.

Approximately 7,000 episodes of television and around 500 movies are expected to be available on Disney+ when it launches later this year. Compared to the newest streaming service's biggest competitor, Netflix, that's not really a whole lot, but Disney certainly has a lot of things that people are going to want to see and material that they won't be able to get elsewhere. This alone should make up for the lack of material at launch time in November. You can check out the first image of Hayley Atwell's Peggy Carter from Marvel's What If...? series below, thanks to the Boardwalk Times Twitter account.

Kevin Burwick