The MCU has had some big villains over the years. It began in Phase 1 with the building up of Loki as a commander of the Chitauri and the wielder of the Mind Stone in The Avengers. It then expanded to the murderous robot, Ultron, who wanted to destroy the Earth by crashing a city into it in Avengers: Age of Ultron. That then brought us to the Mad Titan, Thanos, who successfully wiped out half the universe in Avengers: Infinity War.

With the stakes of the MCU rising and the studio embracing the cosmic realm, putting the entire universe at stake, it's hard to imagine where Marvel could go after the Mad Titan is defeated. We know that they have several movies planned after Avengers 4, and they'll need a new big bad to terrorize the Avengers. Who could they possibly use to pose a threat on the same level as Thanos? There have been some apocalyptic events not caused by the Mad Titan, after all. We'll be turning to Marvel Comics to see 20 potential villains who could be the MCU's next big threat. These villains herald from cosmic worlds, new dimensions, or are regular people who have the brain power to combat Earth's Mightiest Heroes.

20 KANG THE CONQUEROR

The best part about Kang the Conqueror is that he doesn't have any impressive powers. Instead, he is just a man from the future who has access to all sorts of powerful tech and equipment. After he got his hands on a time machine, he decided to go back in time and become the ruler of the known universe in different time periods. When he went back to the present day, it took all of the effort from the Avengers to ensure that he never succeeded in his goals. He was even the primary antagonist in LEGO Marvel Superheroes 2.

It's easy to see why a character like Kang the Conqueror could work in the MCU. If different movies in Phase 4 take place at different points in time, teases to Kang's arrival could be sprinkled throughout. It would all build up to him coming to the present day to take on the Avengers and the Guardians of the Galaxy in one fell swoop. There are also some iconic moments in the comics that would look beautiful on the big screen. Time travel is one concept the MCU hasn't messed with much, and Kang is definitely the best way to introduce it.

19 GALACTUS

Galactus is one of the most powerful beings in the Marvel Universe. Being one of the Celestials, Galactus is often portrayed as a villain more than a god. He is known as the Eater of Worlds because he travels across the universe and consumes entire planets without a second thought. He has a herald in the form of the Silver Surfer who warns every planet that Galactus is coming for a meal. Due to his raw power, he has often fought many of the Marvel heroes at one time and he's been rarely defeated.

The only thing that could get in the way of Galactus coming to Earth in the MCU would be the film rights. As of right now, FOX has the film rights to the character (Galactus is a Fantastic Four villain technically), so it would take some expert dealing on Disney's part to bring that character home as well. If any sort of deal is struck, then we could easily see Galactus wage war on the Avengers and the Guardians of the Galaxy. It would also fit nicely with the Celestials that Marvel has subtly hinted at in the movies, and just seeing this giant cosmic god on the big screen (as something other than a weird gas cloud) would be worth the price of admission.

18 MAGUS

The Russo Brothers have already confirmed that Adam Warlock won't be appearing in Avengers 4, but he is technically in the MCU, being created by the Sovereign at the end of Guardians of the Galaxy Vol. 2. This has led many to speculate that he'll be making his big screen debut in Guardians of the Galaxy Vol. 3. By introducing a character as big as Adam Warlock, it opens up a lot of opportunities for foes that the Avengers can face after Thanos meets his end.

In the comics, Adam Warlock split his personality so that he could become a purely neutral being. However, his evil side started to get smart and wanted to conquer the world for himself. Called the Magus, this version of Adam Warlock sought the Infinity Gauntlet for himself and was willing to kill any hero that stood in his way. This could work in the MCU as a sequel to Thanos' arrival as well as offering another cosmic tie-in to the universe. On top of that, it could serve Adam Warlock's character, giving him the opportunity to express his inner demons. They could also take the route of having Adam Warlock become evil and turn into the Magus to cause trouble.

17 THE CELESTIALS

In Guardians of the Galaxy, we learned just how big the MCU was. There were several beings who existed before life populated the universe, and these characters were the original ones who wielded the Infinity Stones. However, centuries went by and many of them are no longer around. They are known as the Celestials, and they are basically the gods of the Marvel Universe. We got a better look at their power in Guardians of the Galaxy Vol. 2 when it was revealed that Star-Lord's father, Ego the Living Planet, was one of the Celestials.

Considering that the Guardians were able to take down Ego, that could've triggered a series of events that would get the remaining Celestials' attention and possibly have them looking to exact their own revenge. Being massive and powerful beings, it would also allow for a much more interesting battle between the Avengers. It's far beyond just having them fight foot soldiers around the same size as them. This would be a few planet-sized entities with power unlike anything else in the universe. Considering that most of the Celestials are dead in the MCU, it might be a bit of a stretch to expect Marvel to bring them as an antagonistic role, but we'd be so down to see it.

16 MEPHISTO

If you think Loki is a master manipulator and strategist, then you clearly don't know anything about Mephisto. This character is a demon who was created solely as an evil entity, and because of this, he has done some of the most sinister acts in the Marvel Universe. He was the one responsible for taking Johnny Blaze's soul and turning him into the Ghost Rider. Being a more supernatural being, he has all sorts of magical powers that the Avengers aren't prepared to handle. The most terrible thing Mephisto ever did was be the subject of "Spider-Man: One More Day" and cause an unnecessary reboot for Peter Parker.

Mephisto could easily be integrated into the MCU through Doctor Strange. The Sorcerer Supreme deals with beings from different dimensions all the time, so it wouldn't be crazy to think that Mephisto would be the ruler of one of them and be orchestrating the pieces for him to take over the world. Mephisto has the ability to create life, so he could easily create some powerful henchmen on a similar level to the Children of Thanos. Using a demonic character like this would open a lot of opportunities for a future Avengers movie.

15 DORMAMMU

Dormammu is the ruler of the Dark Dimension and one of the greatest foes of Doctor Strange. Being one of the most powerful beings in the Multiverse, Dormammu is constantly thinking of strategies to defeat the Sorcerer Supreme and take over the Earth. He has teamed with other supernatural beings in order to get ahead. In the comics, Dormammu was often heralded as an entity that not even the Ancient One could defeat, meaning that Doctor Strange would have his work cut out for him.

Dormammu is a candidate that we feel could be extremely likely to appear as a more central antagonist in the future of the MCU. The character already appeared in 2016's Doctor Strange. Instead of defeating him, Strange just used the Time Stone to get him stuck in an unbreakable time loop that could only be ended by him leaving the Earth and remaining trapped in the Dark Dimension. It's likely that Dormammu would like to get revenge on the Sorcerer Supreme, and if Marvel decides not to make Doctor Strange 2, it would feel wasteful to never use Dormammu after that. What better role for such a massive villain to have than the big bad of the Avengers?

14 THE INHERITORS

If you're familiar with big Spider-Man events in the comics, then you might be familiar with the Inheritors. This group of villains was hunting down the "totems" across several universes that caused them to go through and kill each version of Spider-Man. This led to portals being opened between universes and the various Spider-Men all going to the same room and teaming up to bring down the Inheritors. While they eventually won, many of the Spider-Men died, including a few that readers had grown to love over the past several years.

The Inheritors would probably need some tweaking before adapting them to the MCU. They would have to function similar to the Children of Thanos, but have a much more main and antagonistic role (as well as put up a serious fight). Because setting up "Spider-Verse" in the MCU would take quite a while, it might be more efficient for Marvel to use them as Avengers villains. They could travel to various locations in the universe and kill a few heroes to spur the forming of Earth's Mightiest Heroes once again. Have them kill a few people in space and get the attention of the Guardians of the Galaxy too.

13 MISTRESS DEATH

We'll admit, this one is a serious long shot. Mistress Death was the physical embodiment of death in the comics. She ruled the world in her own realm. She also managed to gain the attention of the Mad Titan, Thanos. Falling in love with her, he was motivated to kill half of the universe just to impress her. However, she did not appear in Avengers: Infinity War in favor of giving Thanos a much more relatable and understandable motivation and thought process.

If Mistress Death were going to be placed in the MCU, she would also need some changes to her character in the same way Thanos was altered. Marvel would also risk having audiences confuse her with Hela, the Goddess of Death, so they would need to play their cards well. On top of that, some work would need to be done to make her a much better villain than most of the Phase 1 and Phase 2 bad guys. We're not saying she couldn't work as an Avengers villain, but it's unlikely. One possible route they could go is, after the Avengers save all the people who died from the Gauntlet, she could be motivated to strike back.

12 MAESTRO

The future is a scary place in comics, and Maestro is proof of that -- he's a version of Hulk from the future. Most of the people in the world (including the heroes) were wiped out with a nuke and Hulk survived. In order to restore the Earth back to order, he took the name Maestro and decided to rule the world. He kept various objects held by other heroes around his throne room (and even wore some of them). He wasn't the smart and gentle Bruce Banner anymore, instead he was a cold and calculating version of the Incredible Hulk.

Considering that the Hulk is going through an arc that will end in Avengers 4, it's unclear what Marvel will do with him afterward. If they decide to keep him around, it's possible that they could adapt Maestro, giving the Hulk a much newer (and equal) challenge on the heels of losing to Thanos. It would also require the intervention of the rest of the Avengers to take down this stronger version of the Hulk. Furthermore, it could also create some character conflict between Banner and the rest of the team, as they wonder if he really is one of them.

11 DOCTOR DOOM

Doctor Doom is one of the most popular and well-written villains Marvel has created to date. Unlike most bad guys, Doom actually accomplished his initial goal -- his home country of Latveria was under some hard times, so he took over in order to make it prosper once again. While he does have some mixed ideals to say the least, there's a lot of points that he makes that are quite sensible. He then decides that he wants to expand his rule so that the entire world can experience the same level of prosperity that Latveria has.

Doctor Doom is, unfortunately, one of the characters that Marvel sold the movie rights to FOX, being a Fantastic Four villain and all. That said, one could imagine how amazing an Avengers movie would be with Doctor Doom and Latveria at the crux of it all. There could be an all-out war between the Avengers and the Doombots. Doctor Doom could come to New York and gain the love of the people. The possibilities of the character are endless, and it would be all too easy to have him appear as a recurring villain. Marvel could even have him sit in his chair for several films.

10 THE BEYONDER

One of the strongest entities in the Marvel Universe is known as the Beyonder. He is simply the manifestation of what exists beyond the known universe. His presence is what resulted in Molecule Man, one of the deadliest villains to date, getting his awesome powers. There is no limit to what can be done with such a cosmic character that we would love to see him appear on the big screen. The Beyonder's powers can also be taken and used by other characters under the right circumstances, making him that much more threatening.

If Marvel uses the Beyonder, it would be easy to introduce him in another Thor or Guardians of the Galaxy movie. He could be the antagonist that the Avengers defeat on one occasion. The biggest potential with the Beyonder is that, in the post-credits scene, Marvel could have Doctor Doom appear and take the Beyonder's power, thus leading into the next Avengers film -- an adaptation of the new "Secret Wars" complete with its own Battleworld and characters from multiple universes. They could even take the opportunity to briefly bring back some older Avengers. The possibilities are endless with the Beyonder!

9 SINISTER SIX

The Sinister Six are a team of villains that banded together to fight Spider-Man. More often than not, they are led by Doctor Octopus, and the team usually consists of characters like Sandman, Rhino, and Mysterio. Considering that these characters (as far as we know) are on the table for Marvel (they're in talks for using Mysterio), it wouldn't be that difficult to see them appear. However, the team would need some altering if they're going to be a threat for the Avengers as opposed to just Spider-Man, particularly in the power level department.

Spider-Man: Homecoming already teased the Sinister Six's arrival during its post-credits scene where Adrian Toomes and Mac Gargan are having a conversation -- it would be a natural next step to start moving the pieces to include them in the MCU. Marvel could throw in Norman Osborn and potentially give them some added powers or tech to make them too big of a threat for Spider-Man to handle by himself. While, if we had to choose, we'd definitely think that the Sinister Six would appear in a Spider-Man: Homecoming sequel, it would be a fun idea to see them go against the new roster of Avengers following Infinity War and Avengers 4. 

8 ANNIHILUS

In the Marvel Universe, there exists a realm known as the Negative Zone. This alternate dimension is a terrifying world where all sorts of nasty creatures are developed. It was also where Tony Stark created a prison in "Civil War", and he sent all of the locked-up heroes there to rot for not signing on with the government. However, the Negative Zone didn't exist just to take people in -- it could also spit people out. That brings us to Annihilus, a being born of the Negative Zone with the drive to destroy all life in the universe.

During the "Annihilation" event, he got his hands on the Power Cosmic and chained up Galactus. With the help of Thanos, he laid waste to Xandar and the Negative Zone, and attempted to remove all life from both of those worlds. It was up to a small team of heroes (most of which were from the Guardians of the Galaxy) to bring him down. This is something that could easily work in the MCU. If Thanos doesn't die in Avengers 4, it would also give Marvel the opportunity to bring him back as well. There would need to be some tweaking to fit in the large roster of Avengers, but it's a concept that could work well.

7 ONSLAUGHT

Onslaught is a bit of a controversial character (mostly due to his design). However, the story behind his creation is quite interesting. After Magneto caused a lot of problems for the X-Men, Charles Xavier wiped out his mind. However, Xavier's flaws started merging with Magneto's. After a while, the dark sides of both minds combined and a much more powerful being was created with the telepathic abilities of Charles Xavier and the raw power of Magneto. Onslaught was so powerful that the Avengers had to intervene to help save the day.

There are a few reasons why Onslaught wouldn't appear, the biggest one having everything to do with the movie rights to the characters. It'll be a while before Marvel can use the X-Men, and we're not even guaranteed that they would adapt FOX's version of the characters. It would almost feel disingenuous to reboot the X-Men and immediately launch them with an Onslaught story arc. They could alter the villain's origin by having him be composed of different characters (or use the Red Skull to do something involving Red Onslaught), but that's probably the only way we'll see the big time villain on the big screen after Phase 3.

6 THE SKRULL EMPIRE

The Skrulls are one of the nastiest alien races in the Marvel Universe. Having waged war with the Kree several times over, they have always been a problem and the Avengers/Guardians of the Galaxy have had to deal with it. The Skrulls have already been confirmed to appear in Captain Marvel, though we're not sure what form they'll take. This also does some with an asterisk, as the rights to the Super Skrull remains with FOX. That said, there is still a lot of potential in introducing the Skrulls.

First of all, it wouldn't make a lot of sense for Marvel to introduce the Skrulls, have them appear in the '90s, and then never bring them up again. Perhaps Captain Marvel will begin to set up a series of events that lead to an adaptation of "Secret Invasion, essentially, depicting the Skrull coming to Earth and taking the form of several heroes and villains (including taking their powers). It's something that could be quite unsettling for the MCU that would serve it well. It would also make sense, as Marvel could inject a post-credits scene in Captain Marvel that would lead to us believing that the Skrulls are playing the long game.

5 THE MASTERS OF EVIL

The Masters of Evil is something that Marvel hasn't really touched, which is quite a shame. The Masters of Evil are a team of supervillains who unite with one goal in mind: To bring an end to the Avengers. They have a rotating cast of members, but they've been orchestrated by characters like Ultron and Baron Zemo. While the Masters of Evil rarely win the day, it would be an exciting change in strategy to see the Avengers go against a team of villains all similar in power to them.

That said, the Masters of Evil would also need some tweaking in order to fit with the MCU. One possible route Marvel could use is by taking villains who have already appeared in the MCU and having post-credit scenes similar to how Nick Fury brought the Avengers together in Phase 1, but this time it's the villains that are getting together. Some people thought that the use of Baron Zemo in Captain America: Civil War would eventually lead to a live-action version of the Masters of Evil, which didn't happen. Still, having a team of classic villains take on the Avengers would be a smart way to follow up Thanos.

4 KORVAC

Michael Korvac was a brilliant man in an alternate universe. However, his whole life was changed when the Badoons invaded his planet and conquered it. At that point, he saw his opportunity and sided with the Badoons, who then turned him into a cyborg. He eventually beat the Badoons and met up with Galactus, which resulted in him gaining the Power Cosmic. After that, Korvac turned himself into a god with an ethereal appearance and a power set that was unmatched by just about anyone in the galaxy.

Korvac would be a decent villain to use in the MCU following Thanos. Now that both Thor and the Guardians of the Galaxy are willing to embrace the weirder side of Marvel history, Korvac could definitely be set up in one of their films (he was fought by them in the comics after all). We could even see him eventually gain the Power Cosmic, which he then uses to take on Earth, which spurs the intervention of the rest of the Avengers on the planet. It could also work as a tie-in to Galactus, as we learn about the Celestial, who could become a later villain in the MCU by targeting Earth.

3 THE HOOD

There isn't much to the Hood -- he's just a regular man who got swept up in some terrible yet amazing things. Both his father and mother were absent, so he ended up having to take care of himself from a young age. In order to make ends meet, he took up petty crimes and got really good at them. One mission involved him finding a strange pair of boots and a cape that belonged to a demon. Wearing them for himself, he gained the powers of levitation and invisibility. After that, he became one of the best criminals in the Marvel Universe.

From there, the Hood did some crazy things. Not only did he start his own Crime Syndicate, but he would later go on a mission to steal the Infinity Stones from each member of the Illuminati across the entire world. It's these moments that would work well in an Avengers movie (it'd work as a nice follow up to Infinity War). It would also be quite interesting to see Earth's Mightiest Heroes bested by someone who was no more than a regular man. He also has a cool costume that would, no doubt, be pleasant to see on the big screen.

2 NORMAN OSBORN

Norman Osborn is one of the darkest and most insane villains in the Marvel Universe. Having all the money and tech in the world he needs, he's essentially an evil Tony Stark with a much more dangerous attitude. He became the Green Goblin and one of Spider-Man's most powerful foes of all time (he was the one who killed Gwen Stacy). However, that wasn't the only crazy thing that Osborn ever did. He was known for becoming the President of the United States, starting his own version of the Avengers, and even killing other people who took the name of "Goblin."

While Norman Osborn has yet to appear in the MCU, that's something that can easily be changed. Considering that Spider-Man: Homecoming 2 is currently slated for release a few months after Avengers 4, it just might be the kickstart Marvel needs in order to set up a main antagonist for Phase 4. We could see Norman Osborn become the President and start the Dark Avengers to guard the world and outlaw the regular Avengers, which would also mirror how the government treated Steve Rogers. The movie could then be called "Avengers: Dark Reign" -- it basically writes itself at that point!

1 TASKMASTER

Taskmaster isn't the biggest villain the MCU has to offer, but he is one of the deadliest. Being injected with a Super Soldier serum of sorts, he can rival just about anyone in combat. Taskmaster has the innate ability to watch how anyone fights and immediately replicate and predict their attacks. He developed his own school where he would teach others to read fighting styles and has been a villain of the Avengers for several years. Not only that, but he has a frightening yet cool costume to boot.

Taskmaster could be a character who rises up after the events of Avengers 4. After developing a school and appearing in one of the Phase 4 movies, he could then be the central antagonist for the Avengers. If Marvel really wanted to go all out with Taskmaster, they could also make him the leader of the Masters of Evil or the Sinister Six. He would have trained every other villain on that team to learn how to read attacks, so they would be a nearly unstoppable force. It would require the Avengers to think out of the box and probably rely on the Guardians of the Galaxy to teach them how to be more unpredictable.