- "Time. Space. Reality. It's more than a linear path. It's a prism of endless possibility, where a single choice can branch out into infinite realities, creating alternate worlds from the ones you know. I am the Watcher. I am your guide through these vast new realities. Follow me, and ponder the question... What if?"
- ―The Watcher[src]
What if instead of Steve Rogers, Peggy Carter (Hayley Atwell) actually became the first Super Soldier? That creative brainstorming exercise is the heart of What If...?, the Marvel Cinematic Universe's first animated series. The anthology reimagines numerous major events from the movies in game-changing ways, and also features Chadwick Boseman, who was able to reprise T'Challa via voice work before his death.
The fall of He Who Remains at the hands of Sylvie Laufeydottir and Kang the Conqueror's subsequent takeover of the Time Variance Authority has allowed the Sacred Timeline to spur countless branches, effectively destabilizing the Multiverse. From his observatory in the Nexus of All Realities, Uatu would begin to observe the numerous timelines spawned from their various nexus events. However, Uatu himself cannot interfere with events occurring within the realities, having sworn an oath shared among all other Watchers.
Uatu visits eight realities that diverged from the main universe:
- Steve Rogers is seriously wounded in the midst of his transformation into a super soldier, forcing Peggy Carter to take the serum instead.
- Instead of Peter Quill, the Ravagers mistakenly abduct T'Challa from Earth, who would go on to reform the criminal syndicate into a charitable force admired by many.
- Hank Pym assassinates candidates of the Avengers Initiative in his grief after losing his daughter, who was an Agent of S.H.I.E.L.D..
- Doctor Strange turns to dark magic to alter the past and resurrect his girlfriend Christine Palmer after she tragically dies in a car accident, albeit with dire consequences.
- The mission to rescue Janet van Dyne from the Quantum Realm goes terribly awry when Hank Pym returns with a catastrophic zombie apocalypse instead.
- Erik Killmonger saves Tony Stark from a Ten Rings kidnapping attempt as part of his plan to enter Wakanda, manipulating it and the United States into a war.
- Without a brother to grow up with, Thor becomes a rambunctious adult who throws wild and destructive parties across the cosmos.
- Taking up a new vibranium body and the six Infinity Stones, Ultron achieves his vision of universal omnicide after a cataclysmic conquest.
While observing Ultron's universe, the omnipotent AI detects Uatu's presence. Ultron's omnicidal ambitions threaten the Multiverse as a whole, forcing Uatu to violate his oath and recruit Strange, Carter, T'Challa, Killmonger and Thor from their respective universes, along with Gamora in a timeline where she had killed Thanos. In an effort to destroy his Infinity Stones, the newly-formed Guardians of the Multiverse confront Ultron and steal his Soul Stone before leaving for his home reality, where they recruit its last survivor, Natasha Romanoff. Ultron confronts the Guardians again, reclaiming the Stone and subduing them. But Romanoff and Carter upload Arnim Zola into him, who takes over his body. Killmonger and Zola then fight for control of the Stones, forcing Strange to contain them within a pocket dimension.
With Ultron defeated, the Guardians return to their home realities, with the sole exception of Romanoff. Unable to restore her reality, Uatu transports her to the third universe instead, where she joins Nick Fury's new Avengers in their fight against Loki.
- Jeffrey Wright as Uatu/The Watcher
- Hayley Atwell as Peggy Carter/Captain Carter
- Sebastian Stan as Bucky Barnes / Bucky Barnes/Winter Soldier
- Dominic Cooper as Howard Stark
- Stanley Tucci as Abraham Erskine
- Toby Jones as Arnim Zola / Arnim Zola
- Bradley Whitford as John Flynn
- Ross Marquand as Johann Schmidt/Red Skull / Ultron
- Darrell Hammond as General Roeder
- Chadwick Boseman as T'Challa/Star-Lord / T'Challa/Black Panther / T'Challa/Black Panther
- Michael Rooker as Yondu Udonta
- Josh Brolin as Thanos
- Benicio del Toro as Taneleer Tivan/Collector
- Kurt Russell as Ego
- Ophelia Lovibond as Carina
- Carrie Coon as Proxima Midnight
- Tom Vaughan-Lawlor as Ebony Maw / Ebony Maw
- Karen Gillan as Nebula / Nebula
- Djimon Hounsou as Korath the Pursuer
- John Kani as T'Chaka / T'Chaka
- Sean Gunn as Kraglin Obfonteri
- Chris Sullivan as Taserface
- Seth Green as Howard the Duck / Howard the Duck
- Danai Gurira as Okoye / Okoye / Okoye
- Samuel L. Jackson as Nick Fury / Nick Fury / Nick Fury
- Jeremy Renner as Clint Barton/Hawkeye / Clint Barton/Hawkeye / Clint Barton/Hawkeye
- Mark Ruffalo as Bruce Banner/Hulk / Bruce Banner/Hulk
- Tom Hiddleston as Loki / Loki
- Clark Gregg as Phil Coulson / Phil Coulson
- Jaimie Alexander as Sif / Sif
- Frank Grillo as Brock Rumlow / Brock Rumlow / Brock Rumlow
- Lake Bell as Natasha Romanoff/Black Widow / Natasha Romanoff/Black Widow / Natasha Romanoff/Black Widow
- Mick Wingert as Tony Stark/Iron Man / Tony Stark / Tony Stark/Iron Man / Tony Stark/Iron Man / Tony Stark/Iron Man
- Benedict Cumberbatch as Stephen Strange/Doctor Strange / Stephen Strange/Doctor Strange
- Rachel McAdams as Christine Palmer
- Benedict Wong as Wong
- Tilda Swinton as Ancient One
- Ike Amadi as O'Bengh
- Leslie Bibb as Christine Everhart / Christine Everhart
- Paul Bettany as Vision / J.A.R.V.I.S.
- Evangeline Lilly as Hope van Dyne/Wasp
- Paul Rudd as Scott Lang/Ant-Man
- Jon Favreau as Happy Hogan / Happy Hogan
- Emily VanCamp as Sharon Carter
- David Dastmalchian as Kurt Goreshter
- Hudson Thames as Peter Parker/Spider-Man
- Michael B. Jordan as Erik Stevens/Killmonger
- Angela Bassett as Ramonda
- Andy Serkis as Ulysses Klaue
- Don Cheadle as James Rhodes
- Chris Hemsworth as Thor
- Natalie Portman as Jane Foster
- Kat Dennings as Darcy Lewis
- Jeff Goldblum as En Dwi Gast/Grandmaster
- Cobie Smulders as Maria Hill
- Taika Waititi as Korg
- Alexandra Daniels as Carol Danvers/Captain Marvel / Carol Danvers/Captain Marvel / Carol Danvers/Captain Marvel
- Rachel House as Topaz
- Josh Keaton as Steve Rogers/HYDRA Stomper / Steve Rogers/Captain America / Steve Rogers
- Georges St-Pierre as Georges Batroc
- Neal McDonough as Dum Dum Dugan
- Isaac Robinson-Smith as Brick
- Fred Tatasciore as Drax / Corvus Glaive / Volstagg / Drax
- Maddix Robinson as Young T'Challa
- Brian T. Delaney as Peter Quill
- Michael Douglas as Hank Pym/Yellowjacket
- Stephanie Panisello as Betty Ross
- Mike McGill as Thaddeus Ross / Thaddeus Ross
- Kiff VandenHeuvel as Obadiah Stane
- Beth Hoyt as Pepper Potts
- Ozioma Akagha as Shuri
- Josette Eales as Frigga
- David Chen as Hogun
- Max Mittelman as Fandral
- Clancy Brown as Surtur
- Cynthia McWilliams as Gamora
|What If... Captain Carter Were The First Avenger?||1.01||August 11, 2021||A.C. Bradley||Bryan Andrews|
|When Steve Rogers is seriously injured, Peggy Carter becomes the world's first Super Soldier.|
|What If... T'Challa Became a Star-Lord?||1.02||August 18, 2021||Matthew Chauncey||Bryan Andrews|
|The rough-and-tumble space pirates known as the Ravagers abduct T'Challa instead of Peter Quill.|
|What If... The World Lost Its Mightiest Heroes?||1.03||August 25, 2021||A.C. Bradley & Matthew Chauncey||Bryan Andrews|
|Nick Fury struggles to launch the Avengers when candidates are targeted by a serial killer.|
|What If... Doctor Strange Lost His Heart Instead of His Hands?||1.04||September 1, 2021||A.C. Bradley||Bryan Andrews|
|A grief-stricken Doctor Strange uses the Eye of Agamotto in a dangerous effort to change the past.|
|What If... Zombies!?||1.05||September 8, 2021||Matthew Chauncey||Bryan Andrews|
|When the Avengers are infected by a zombie plague, surviving heroes search for a cure.|
|What If... Killmonger Rescued Tony Stark?||1.06||September 15, 2021||Matthew Chauncey||Bryan Andrews|
|An American soldier called Killmonger rescues Tony Stark when his Humvee is attacked in Afghanistan.|
|What If... Thor Were an Only Child?||1.07||September 22, 2021||A.C. Bradley||Bryan Andrews|
|Thor, who never learned to be a good hero, throws an out of control intergalactic party on Earth.|
|What If... Ultron Won?||1.08||September 29, 2021||Matthew Chauncey||Bryan Andrews|
|Natasha Romanoff and Clint Barton seek to destroy killer-robot Ultron following a cataclysmic event.|
|What If... The Watcher Broke His Oath?||1.09||October 6, 2021||A.C. Bradley||Bryan Andrews|
|What If... The Watcher Broke His Oath?|