5 Marvel Characters Who Could Betray The Avengers In Doomsday

Besides bringing certain doom to the Marvel Cinematic Universe in "Avengers: Doomsday," there's also a mild pang of fear that Doctor Doom (Robert Downey Jr.) could spark dissension among the ranks of heroes who are going to do their best to save the Multiverse, and among the others who are getting pulled into the mix. The world isn't what it was after the events of "Avengers: Endgame." Characters aren't simply heroes or villains. As a result, a handful of characters could end up standing on Doom's side before the credits roll, and we have our suspicions about who they might be.

It's nothing new for heroes or villains to rethink their actions and switch sides in a last-minute shock. Tom Hiddleston's Loki, for example, was a repeat offender until he finally learned his lesson in the Disney+ show. Still, plenty more players in this upcoming game of comic book movie death could stab Earth's Mightiest Heroes in the back. Combining our knowledge of the Marvel universe with the cinematic one we've loved since 2008, here are our five guesses for who could, at the last minute, throw a wrench in the works and make things worse than they already are. Such a shift in tactics could see these characters on board for whatever Doom has planned, or simply making sure they get out of this reality-wrecking ordeal alive. 

To start things off, we're going with a relatively new MCU character who became a major problem when he arrived in 2022. Tenoch Huerta's Namor stayed true to his source material and proved to be another complex character who kept his people's interests in mind. Sadly, that meant going up against an already rattled Wakandan Empire following the death of T'Challa (Chadwick Boseman), leading to the deaths of hundreds, including Queen Ramonda (Angela Bassett). By the end of the film, Shuri (Letitia Wright) might've drawn a line in the sand between the two warring nations, but that doesn't mean it'll last in "Avengers: Doomsday."

From what we can see in the trailers, Namor definitely seems to have a presence in the new sequel, but it's unclear where his allegiance will lie and for how long. In the comics, Sub-Mariner has found himself on both sides of good and evil over the years, even forming alliances with Doom from time to time. Their partnership has remained a constant test, though, with both regularly trying to manipulate the other for their own gain. With that in mind, could the same happen here, and could Namor find himself in league with the Latverian leader to ensure Talokan's safety? If so, we anticipate that whatever bargain they make won't last long, and Namor will regret his decision by the end of it, before shouting "Imperius Rex" and cursing Doom's name like the rest of us.

If one player in this upcoming throwdown is more of a flight risk than Namor, it's the one who's been consistently untrustworthy since 2003 (and who we occasionally back). Erik Lehnsherr, aka Magneto (Ian McKellen), has always been about the benefit of mutantkind, which has kept him at odds with his longtime friend and nemesis, Charles Xavier (Patrick Stewart). With that in mind, it makes sense that when the Avengers travel to his Earth and learn what's at stake, along with the rest of the X-Men, his last defense will be desperate, with casualties as a minor concern.

We can't forget that Erik has proven time and again that his mutant brothers and sisters sacrificing themselves has often been necessary (in his eyes, at least) for the good of homo superior. As a result, it would make total sense for him to throw these briefly visiting heroes into the meat grinder if it means his Earth makes it through safely. There's also a chance that, as powerful as he is, Erik might believe he's strong enough to take Doom on alone, which lines up with what's already leaked online.

Back in 2025, Ian McKellen let slip that he was involved in a big battle sequence for the upcoming sequel, and all released footage suggests he could either be the last line of defense against Doom or selfishly go into battle and do more harm than good. As far as we can tell, it's anyone's guess, but we can guarantee it'll be a superhero scrap worth watching.

Hard as it might be to believe given his time in the big-screen franchise, Hank McCoy, aka Beast (Kelsey Grammer), hasn't had the cleanest record over the years. Not only have dark versions from alternate realities (like the one that'll appear in "Doomsday") caused all kinds of chaos, but even the main one has gone flat-out bonkers, creating clones of himself and committing evil deeds under the radar of those he once called friends. With that in mind, it would make for an impressive plot twist (if the movie does indeed have one) if, instead of the Master of Magnetism sticking to his M.O., the legendary X-Men hatches a scheme to ensure Earth survives this massive ordeal, even if the others don't.

While it might shock some, this revelation fits with the events that led up to this point. Let's not forget that Beast has already appeared in the MCU in "The Marvels" post-credit scene, establishing that he's had plenty of time to prep for this upcoming event and may have settled on only one solution. It wouldn't be anything new for Grammer, either. He's played a handful of villains in the "Transformers" franchise, as well as the legendary, box-fresh bad guy, Stinky Pete, in "Toy Story 2." Could you imagine seeing this longtime hero turn heel? Doing so could also set up an air of uncertainty if another variant of his character arrives in the newly formed "X-Men" that are set to arrive in 2028.

We might've left with him on the winning side at the end of "Thunderbolts*," but just like a lot of characters on this list, historically speaking, John Walker's allegiances have been known to sway in various directions over the years in the comics. This worn-down super soldier has spent most of his time in the shadows of both Sam Wilson and Steve Rogers in Marvel's history, which was a point of focus during his time in "Falcon and the Winter Soldier," but what if that mean streak of envy reappears when he's forced to see the much-loved star-spangled hero and the original shield wielder return and give orders for this new mission? Could Walker's pride once again get in the way of his duty, and if so, could Doom exploit that to work in his favor?

What if, in Doom's plans for rewriting history, he offers Walker the appointment as the new Captain America? If so, might Walker's old flaws resurface, and he might take up the offer? If so, it would undoubtedly lead to the one man with the shortest term as the nation's hero making some tough decisions and undoing every past deed he'd previously redeemed himself of. Of course, we hope that isn't the case, and that this rough-around-the-edges New Avenger stays on the straight and narrow, but admittedly, seeing him bend as easily as his shield does under Doom's pressure seems just as likely. No offense, John.

A whole host of super-powered players could change the game in "Avengers: Doomsday" besides the ones we've listed, but none could cause the same world-ending damage as someone who's already come close to doing so. Bob (Lewis Pullman) proved a force to be reckoned with in "Thunderbolts*" when he took on the mantle of The Sentry, becoming one of the most powerful beings in the universe and able to alter reality itself. However, such limitless ventures only came about when The Void took over Bob and was only kept at bay via the power of (checks notes) friendship.

What happens, though, if Bob's support group heads off into different realities, leaving him to hold the fort on Earth-616? Might Doom pay a visit and push all the wrong buttons, sending The Sentry into panic mode? If so, Bob might betray the Avengers, but not of his own choosing, and The Void could take over again, saving Doom the hard work of wrecking a world by letting one of their own do it for him. We hope that isn't the case, though, and unlike previous incidents involving mega-powerful players like Captain Marvel or The Hulk, The Sentry gets a long time off the bench and proves just how powerful he is in the fight against Doom, with zero involvement from The Void. For now, we'll have to wait and see who turns their back on our heroes when "Avengers: Doomsday" arrives in theaters on December 18.