Marvel Studios first animated series brings together an epic cast from across the first three phases of the MCU, although fans may notice one significant substitute in this week's episode.
Marvel's What If episode six takes us to an alternate version of Tony Stark's traumatic superhero origin story, where instead of being abducted by the Ten Rings, he is rescued by Erik Killmonger and thus never becomes Iron Man.
While Black Panther star Michael B Jordan did return to voice his iconic villain, Robert Downey Jr is swapped out by voice actor Mick Wingert in the action-packed chapter.
Previously, executive producer Brad Winderbaum had discussed the challenging of recasting certain MCU roles in cases where the original stars were not available to return.
"In the cases where we couldn't get the original voice actors back, many of which were very iconic roles with very identifiable voices, we prioritised the performance over the soundalike," he tells ComicBook.com.
"So you might be able to achieve a perfect Tony Stark voice, but if the depth of the character wasn't there and the acting or performance didn't have dimensionality to it, it wouldn't matter. You'd be taken out. That would take you out."
That said, the team behind What If has done a good job reuniting a large number of MCU cast members, including Samuel L. Jackson, Chris Hemsworth and Hayley Atwell.
This is also the final posthumous release for Chadwick Boseman, who features in several episodes as T'Challa, having recorded dialogue before his tragic death in 2020.
Read on for your guide to the star-studded cast of Marvel's What If...? – including who voices Steve Rogers – and if you want to brush up on the MCU so far in preparation for these fresh twists, check out our complete guide to the Marvel movies in order.
Jeffrey Wright plays Uatu the Watcher
Who is The Watcher? The Watcher comes from an alien race of near-immortal beings, whose purpose it is to witness and record the events of the Marvel Universe. They are sworn never to intervene in what unfolds, no matter how catastrophic, although Uatu has broken this vow on a handful of occasions in the comic books. The Watcher will be our narrator and guide through these strange alternate MCU tales.
What else has Jeffrey Wright been in? Wright has recently starred in HBO's sci-fi drama Westworld. Previously, he played CIA agent Felix Leiter in Daniel Craig's Casino Royale and Quantum of Solace, a role he will soon reprise for this winter's No Time To Die. He is one of several actors to bag roles in both the Marvel and DC universes, as he will soon portray Commissioner James Gordon in next year's The Batman.
Hayley Atwell plays Captain Peggy Carter
Who is Peggy Carter? Peggy Carter was an accomplished agent of the SSR, who played a pivotal role in the success of Project Rebirth – which turned scrawny Steve Rogers into superhero Captain America. The two later fell in love but when they were separated by a wartime mission gone wrong, she went on to become one of the founding members of SHIELD.
In What If...?, The Watcher shows us how things would have been different if Peggy herself had been given the super soldier serum, turning her into Captain Carter – seemingly an alternate version of cult comic book character Captain Britain.
What else has Hayley Atwell been in? Atwell's recent projects include legal drama Conviction, period piece Howards End, and Netflix's suspenseful Criminal: UK. On the big screen, she starred opposite Keira Knightley in The Duchess and Ewan McGregor in Christopher Robin.
Dominic Cooper plays Howard Stark
Who is Howard Stark? The father of Tony Stark, Howard worked alongside Steve Rodgers and Peggy Carter during the Second World War, as seen in 2011's Captain America: The First Avenger.
In What If...?, he fights alongside Captain Carter in an early Iron Man suit, proving that an appreciation for badass armour clearly runs in the family.
What else has Dominic Cooper been in? Cooper played the lead role in supernatural drama Preacher, which aired on Amazon Prime Video in the UK. Previously, he had appeared in The History Boys, Mamma Mia!, Need For Speed and Warcraft.
Mick Wingert plays Tony Stark / Iron Man
Who is Tony Stark/Iron Man? Arguably the MCU's most famous character, Tony Stark was first introduced as a selfish weapons manufacturer, but his outlook on life was radically changed after realising the harm his work was doing to the world. After being kidnapped by an organisation called the Ten Rings, he fought his way out in a suit of armour and later became the superhero known as Iron Man – a founding member of the Avengers.
Marvel's What If...? imagines how things would have gone very differently if Stark had never experienced his traumatic abduction, but was instead rescued by Erik Killmonger.
What else has Mick Wingert been in? This isn't Wingert's first time voicing Tony Stark, as he also took on the role in Lego Marvel Super Heroes: Avengers Reassembled, and Disney XD animated shows Avengers Assemble, Guardians of the Galaxy and Spider-Man.
Sebastian Stan plays James 'Bucky' Barnes / The Winter Soldier
Who is Bucky Barnes? Captain America's wartime pal, who was experimented on by Russian intelligence and transformed into the ruthless assassin known as The Winter Soldier.
In the What If...? trailer, we see Bucky going up against an undead version of Steve Rogers, in a story seemingly inspired by the Marvel Zombies comic books.
What else has Sebastian Stan been in? Recently reprising his Marvel role for Disney Plus series The Falcon and the Winter Soldier, Stan has also starred in I, Tonya and Netflix's The Devil All The Time. He will be seen later this year in hotly anticipated miniseries Pam & Tommy.
Josh Keaton plays Steve Rogers
Who is Steve Rogers? In the main MCU, he's the unlikely soldier who becomes Captain America - though in the first episode of What If...? it's his old love interest Peggy (Hayley Atwell) who gets the super-soldier serum instead, and this Steve becomes an armoured proto-Iron Man called HYDRA Stomper.
What else has Josh Keaton been in? Following original star Chris Evans' departure, the voice role is picked up by voice actor Josh Keaton, who may be familiar to animated superhero fans for his leading role in the critically-acclaimed Spectacular Spider-Man series, as well as roles in TV shows like Marvel's Spider-Man, Marvel's Ant-Man, Justice League Action and many more.
Ross Marquand plays The Red Skull
Who is The Red Skull? A megalomaniacal scientist working for Nazi Germany, Johann Schmidt was the arch-enemy of Captain America in the comics and 2011's Captain America: The First Avenger. He was originally played by Hugo Weaving.
What else has Ross Marquand been in? Skilled impressionist Marquand has voiced the Skull in live-action before, taking over the role from Weaving in Avengers: Infinity War and Endgame. He has played Aaron in live-action on The Walking Dead, and other roles have included work on Mad Men, Impress Me, Deadbeat, The Last Tycoon and Robot Chicken.
Benedict Cumberbatch plays Doctor Strange
Who is Doctor Strange? Doctor Strange is the Sorcerer Supreme of the main MCU reality, charged with guarding it from all manner of magical threats. Formerly, he was an arrogant surgeon who turned to the mystic arts after his hands were irreparably damaged in a car accident. He was an instrumental figure in the war against Thanos and his alien forces, as seen in Avengers: Infinity War and Endgame.
Strange's What If...? episode is a mystery for now, but the trailers have seen him fighting what appears to be an evil version of himself, which could perhaps be setting the stage for next year's Doctor Strange solo film.
What else has Benedict Cumberbatch been in? Cumberbatch rose to stardom playing the title role on BBC One crime drama Sherlock, with subsequent projects including Patrick Melrose, Brexit: The Uncivil War, 1917 and The Hobbit film series.
Chadwick Boseman plays T'Challa / Star-Lord
Who is T'Challa? In the MCU as we know it, T'Challa is the king of Wakanda, who ascended to the throne following his father's assassination in Captain America: Civil War. He also is the nation's protector as the Black Panther, with enhanced strength derived from a heart-shaped herb and a state of the art suit designed by younger sister, Shuri.
In Marvel's What If...?, we will see a different version of T'Challa, who is abducted by galactic scavenger Yondu as a young boy and goes on to become the outlaw known as Star-Lord.
What else has Chadwick Boseman been in? Boseman became one of the world's best-loved stars with his performance in Black Panther, as well as previous acclaimed turns in 42, Get On Up, Da 5 Bloods and Ma Rainey's Black Bottom. Tragically, he passed away in 2020, with Marvel's What If...? being his final posthumous release.
Michael Rooker plays Yondu
Who is Yondu? Yondu is the leader of a band of intergalactic outlaws called The Ravagers. In the main MCU, he abducts Peter Quill from planet Earth as a boy and raises him in outer space, but this series will explore what would have happened if he had kidnapped a young T'Challa instead.
What else has Michael Rooker been in? Rooker played Merle Dixon on zombie drama The Walking Dead, while on the big screen he has recently appeared in F9: The Fast Saga and James Gunn's The Suicide Squad.
Samuel L Jackson plays Nick Fury
Who is Nick Fury? One of the key architects of the Marvel Cinematic Universe, former SHIELD director Nick Fury was the man who made it his mission to assemble the Avengers. As such, he has naturally crossed paths with a number of powerful superheroes, so it's not yet known what moment exactly his episode will focus on.
What else has Samuel L Jackson been in? Jackson is one of Hollywood's biggest stars, with some of his most iconic projects being Jurassic Park, Die Hard with a Vengeance, Pulp Fiction, Snakes on a Plane and the Star Wars prequels.
Jeremy Renner plays Hawkeye
Who is Hawkeye? Former SHIELD agent Clint Barton became The Avengers' resident archer in 2012's first team flick. The character's What If...? episode takes us back to the days when he worked closely with Director Nick Fury.
What else has Jeremy Renner been in? Renner will be back as Barton once again in November for his solo Hawkeye series on Disney Plus. Outside of the MCU, the actor is known for his work on blockbusters Mission: Impossible, The Bourne Legacy and Arrival, as well as award contenders The Hurt Locker, The Town and American Hustle.
Chris Hemsworth plays Thor
Who is Thor? Thor is the God of Thunder. In his younger years, he was deemed unworthy of his enormous power and cast out of Asgard to learn humility, ultimately doing so and becoming a superhero.
Rumour has it that Thor's episode of What If...? will ask what would have happened if his father hadn't taken such decisive action, and instead allowed his son to grow up foolish and reckless.
What else has Chris Hemsworth been in? Breaking out in the cast of Australian soap opera Home and Away, Hemsworth has gone onto become a major Hollywood movie star. Outside of the MCU, you may recognise him from The Cabin in the Woods, Snow White and the Huntsman, 2016's Ghostbusters, Men in Black: International, or Netflix's Extraction.
Tom Hiddleston plays Loki
Who is Loki? Loki is Thor's brother and the God of Mischief. His initial appearances in the MCU were in formidable villain roles, but he has recently taken on the persona of an antihero – as seen in the recent Disney Plus Loki solo series.
It's unclear what exactly Loki will be getting up to in What If...?, but the trailers have shown him leading an army against his brother, perhaps in an alternate bid to take over Earth.
What else has Tom Hiddleston been in? Besides his Marvel work, Hiddleston is known for BBC One thriller The Night Manager, gothic horror flick Crimson Peak, and 2017 blockbuster Kong: Skull Island.
Michael B Jordan plays Erik Killmonger
Who is Erik Killmonger? Killmonger is Wakandan but was raised in Oakland, California by his father, who was sent there to work undercover but ultimately betrayed his homeland and was killed. This put Erik on a path towards revenge which was very nearly successful, as he led a coup of the Wakandan royal family and very nearly killed his cousin, T'Challa. In Marvel's What If...?, Killmonger intervenes when Tony Stark is attacked by the Ten Rings gang, preventing him from being abducted and thus eliminating the need for him to invent his first Iron Man suit. The repercussions are huge.
What else has Michael B Jordan been in? Jordan's star has been on the rise for some time, with his biggest projects to date being found-footage thriller Chronicle, the Creed films, and 2019 legal drama Just Mercy.
Angela Bassett plays Queen Ramonda
Who is Queen Ramonda? Ramonda was the queen of Wakanda, ruling peacefully alongside husband T'Chaka for many years. When he was assassinated, she stepped down from the throne and allowed her son, T'Challa, to take over. In the world of What If...?, we meet Ramonda before her abdication, where she is seen fighting on the frontlines against threats to her country.
What else has Angela Bassett been in? Bassett is one of Hollywood's most established names, with a career that began back in the 1980s. Her recent projects include Olympus Has Fallen, Mission: Impossible – Fallout, American Horror Story, and crime drama 9-1-1.
Jon Favreau plays Happy Hogan
Who is Happy Hogan? Happy is Tony Stark's right-hand man, who was a close friend to the billionaire for decades leading up to his death in Avengers: Endgame.
What else has Jon Favreau been in? Favreau is known for on-screen roles in Swingers, Daredevil, and Chef, as well as for directing mega-hits Elf, The Jungle Book and The Lion King. He portrayed Monica's love interest Pete in the third season of Friends.
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Seth Green plays Howard the Duck
Who is Howard The Duck? In the comic books, Howard The Duck hails from a parallel universe inhabited entirely by anthropomorphic ducks, before being drawn into the mainline Marvel Universe for some truly farcical adventures.
Little his known about his MCU counterpart, who has only had the briefest of cameos in the first two Guardians of the Galaxy films, but we may learn more about him here.
What else has Seth Green been in? Green has lent his voice to animated characters several times before, playing Chris Griffin on Family Guy and various characters on his sketch comedy Robot Chicken. He has also appeared in live-action in Austin Powers and Buffy the Vampire Slayer.
Marvel's What If cast
Here are the actors also included in the epic line-up assembled for Marvel's What If on Disney Plus:
- Mark Ruffalo plays Bruce Banner / Hulk
- Paul Bettany plays Vision
- Josh Brolin plays Thanos
- Don Cheadle plays James Rhodes
- Paul Rudd plays Scott Lang / Ant-Man
- Evangeline Lilly plays Hope van Dyne / Wasp
- Natalie Portman plays Jane Foster
- Jaimie Alexander plays Sif
- Benicio del Toro plays The Collector
- Kat Dennings plays Darcy Lewis
- Michael Douglas plays Hank Pym
- Jeff Goldblum plays Grandmaster
- Clark Gregg plays Phil Coulson
- Danai Gurira plays Okoye
- Djimon Hounsou plays Korath
- Toby Jones plays Arnim Zola
- Kurt Russell plays Ego
- Andy Serkis plays Ulysses Klaue
- Cobie Smulders plays Maria Hill
- Tilda Swinton plays The Ancient One
- Stanley Tucci plays Abraham Erskine
- Emily VanCamp plays Sharon Carter
- Taika Waititi plays Korg
- Benedict Wong plays Wong
Marvel's What If...? premieres on Disney Plus on Wednesday 11th August. You can sign up to Disney Plus for £7.99 a month or £79.90 a year now. Check out more of our Sci-Fi and Fantasy coverage or visit our TV Guide to see what's on tonight.