Brock Rumlow was introduced as a HYDRA agent working undercover for S.H.I.E.L.D. in Captain America: The Winter Soldier, and that movie set the stage for him to become Crossbones. In Captain America: Civil War, the villain did, in fact, take on that moniker, but his time in the MCU was short-lived.
After attempting to blow himself (and Captain America) up, Crossbones was taken out by the Scarlet Witch...and that was that. He did appear in Avengers: Endgame when Earth's Mightiest Heroes travelled back in time to 2012, but that didn't exactly open the door to any sort of permanent return.
Now, in an interview with Variety, actor Frank Grillo has confirmed that after What If?, his time as Crossbones is over. "They’re done with me. Because of the way the stories wound up being told and just how big the stories became, the Crossbones of it wasn’t really part of the future of the Avengers."
This feels like a real missed opportunity on the part of Marvel Studios, especially as Rumlow could have become a recurring threat in Captain America's corner of the MCU. He'd have been a great fit for The Falcon and The Winter Soldier, too, especially as Sam Wilson was responsible for his scarred visage.
It's not going to happen, though, and Marvel Studios is clearly moving on to other villains...
Click on the "Next" button below to see 10 MCU
characters who vanished with no explanation!
10. Nova Prime
Convincing Glenn Close to join the MCU was a big win for filmmaker James Gunn as he developed Guardians of the Galaxy for Marvel Studios.
Her role as Nova Prime was minor, but still crucial to how the story played out. Richard Rider was M.I.A., but the existence of the Nova Corps proved to be more than enough to leave fans chomping at the bit for their MCU future.
Unfortunately, Thanos decimated them off camera in Avengers: Infinity War, so we can only assume Nova Prime was among the fallen. The reason we have to assume that, however, is because Marvel Studios has never bothered to address what became of the interplanetary police force.
Did Thanos leave half of them alive? Are they all dead. Who knows.
9. Aaron Davis
Atlanta star Donald Glover is one of the biggest talents working today, and even those who hated Solo: A Star Wars Story agreed that his take on Lando Calrissian was a highlight.
Bringing the actor into the MCU was huge, but as Aaron Davis (Miles Morales' uncle, and the vigilante known as Prowler), he brought little to the table in Spider-Man: Homecoming. A funny exchange with the inexperienced wall-crawler followed, as did a throwaway mention of Aaron's nephew.
What felt like a perfect way to introduce Prowler and/or Miles in the sequel was completely overlooked, no great surprise when Peter Parker was heading overseas. Unfortunately, Spider-Man 3 looks to be equally unlikely as a platform to bring Aaron back.
What a waste.
8. Betty Ross
Betty Ross is the definitive Bruce Banner love interest, and Liv Tyler did nothing but good work in 2008's The Incredible Hulk.
When that film was released, the plan at Marvel Studios was to have Earth's heroes assemble to fight a Hulk who had fallen under the control of Loki. When Joss Whedon boarded the project, the film was overhauled, and the Green Goliath story played out in an entirely different way.
It's likely Betty was once part of The Avengers, but Bruce moved on to Black Widow, and then left the planet entirely. He's back now, though, and has Bruce's intelligence.
Despite all of that, it seems he's never once looked Betty up. Marvel, meanwhile, has forgotten all about the bond these two share.
7. Dr. Selvig
In the early days of the MCU, Dr. Erik Selvig was a major part of how the stories in this shared world unfolded. He was in Thor, then The Avengers. He was crucial to Thor: The Dark World too, and even showed up Avengers: Age of Ultron.
Avengers: Endgame confirmed he was among those Thanos snapped out of existence, but that means he eventually came back with everyone else. Only Spider-Man: Far From Home has covered the aftermath of the Blip, so Selvig could return, but as it stands, he's still been M.I.A. for going on six years.
When and why did he stop being so important to the MCU?
When Joss Whedon left by the looks of it, and Marvel Studios instead decided that these heroes didn't need the assistance of a big brain like Selvig.
6. Lady Sif
Sif will make her MCU return in Thor: Love and Thunder, though rumor has it Jaimie Alexander might return before then in Disney+ series, Loki.
This marks a long overdue return for the hero, but also leaves us to wonder why Marvel Studios was so quick to move on from the character. She was never as crucial to those first two Thor films as she should have been, and never got chance to explore a romantic relationship with the God of Thunder despite there being a connection between them.
The last time we saw Sif was when she and Volstagg visited The Collector.
Perhaps, instead of returning to Asgard, she chose to traverse the spaceways, and it's there Thor will find her as he travels with the Guardians of the Galaxy?
5. Mitchell Carson
Once a major player in S.H.I.E.L.D., it was later revealed that Mitchell Carson was another undercover HYDRA operative. That was why we saw him in Ant-Man attempting to acquire the Yellowjacket armor.
That plan failed, but he made it out of Darren Cross' building alive to fight another day.
He wasn't completely empty-handed, however, as his briefcase was full of Pym Particles. There's a lot that could be done with those, but there's been no sign in the past six years that Marvel Studios plans to either bring Carson back or reveal what ended up happening to them.
Marvel forgot this character, and created what some might describe as a plot hole as well.
4. Dr. Cho
With the Chinese box office becoming increasingly important, many film studios in the mid-2010s realising that embracing the Middle Kingdom might increase the chances of success in the country.
Iron Man 3 included scenes specifically shot for China, though many filmgoers there took umbrage with the way those were presented. Despite that, Avengers: Age of Ultron still prominently featured Claudia Kim, an actress who is a big star in that part of the world.
As Dr. Helen Cho, she played a crucial role in how the sequel panned out.
Despite being attacked by Ultron, Cho later joined the staff of the New Avengers Facility...and hasn't been since. We don't know what became of her, but she's been forgotten.
3. Abomination
It's worth mentioning Samuel Sterns here because Marvel Studios teased his transformation into The Leader, only to forget all about that villain and do nothing with him.
With no solo franchise for Hulk, perhaps we shouldn't be overly surprised by the disappearance of one of his greatest foes from the MCU. However, leaving a ready-made villain like Abomination behind might be one of the biggest mistakes the MCU has made.
He could have easily fallen into the hands of HYDRA or been used against the Avengers in a film like Captain America: Civil War.
Tim Roth will reprise the role in Disney+'s She-Hulk, but that comes over a decade after he first played this villain. Marvel forgot him for a while, but it seems this is one more character they've finally decided to do something with.
2. Rhomann Dey
It's all too easy to forget just how impressive Guardians of the Galaxy's cast was, with John C. Reilly another big name we never expected to see in the MCU.
As Rhomann Dey, he made a lasting impact, and added even more heart to a film packed full of it.
Like Nova Prime, he's been missing in action since 2014; having him cross paths with the team again in Vol. 2 would have been easy enough. Unfortunately, we're again left to assume that both her, and his family, were victims of Thanos when the Mad Titan attacked Xandar.
We hope there's a future for him in Vol. 3, but only if Marvel remembers him.
1. Dr. Leonard Samson
Ty Burrell became a huge star after starring in The Incredible Hulk thanks to Modern Family, but Marvel Studios still failed to bring the actor back to the MCU as Dr. Leonard Samson.
That's a weird decision, and this psychiatrist could have fitted into any number of films. For starters, he could have been the shrink Tony Stark spoke to at the end of Iron Man 3; albeit transformed into his heroic alter ego as Doc Samson. That would have required more screentime, though, and more than just the cameo he made in 2008.
It seems Marvel never had any serious plans for Samson, with his inclusion being little more than an Easter Egg for fans.
It's no wonder then that he ended up being forgotten.