The Avengers were always a big deal. Today, however, they are a bigger deal than they have ever been before. At one time, the team was considered to be Marvel's version of the Justice League. Given the success of the Marvel Cinematic Universe (and lack of success for DC's equivalent) things are now the other way around.
The Marvel Cinematic Universe is completely centered around the Avengers team. Despite this, there are many important Avengers villains that have yet to appear on the big screen. Although many of these villains will likely soon appear in the MCU, other fans may have to wait for some time to finally see make their cinematic debut.
10 Taskmaster
Although Taskmaster is set to debut in Black Widow's upcoming (and long-delayed) solo movie, the villain does, technically, have yet to appear on the big screen. It's a shame that it has taken this long, given how interesting of a villain Taskmaster truly is.
Without a doubt, Taskmaster will make for a great antagonist for Black Widow to face off with. Hopefully, he (or she, the identity of the MCU's Taskmaster has yet to be revealed) will survive the movie and possibly become an Avengers villain in a future movie.
9 Super-Adaptoid
The Super-Adaptoid has the ability to copy and imitate other superhumans' powers. Upon coming into contact with the Avengers team, the Adaptoid become incredibly powerful and was nearly impossible to defeat.
Although any Avengers movie that included the Super-Adaptiod would likely also need to have a villain mastermind behind the machine, in terms of physical threats, this robotic enemy would be, by far, the most dangerous enemy the superhero team had ever faced in a movie.
8 The Living Laser
Although originally the Living Laser relied on technology and trickery, eventually his entire body was replaced by energy. He was quite literally a living laser. This made the villain one of the most difficult enemies for the Avengers to face.
It's not hard to imagine how big a threat the Living Laster could pose in a live-action Avengers movie. Given the fact that the Avengers can't just physically dispatch with him, the Living Laser would make for a great on-screen antagonist.
7 Hood
In the comics, Parker Robinson came across what is known as a Nisanti demon. Robbins then went on to steal the demon’s cape and boots which then gave Robbins incredible powers. With these new abilities, he then went on the become a powerful crime boss named the Hood.
There are very few Avenger villains that are like the Hood. In fact, he really is a one of a kind bad guy in almost every conceivable way. Following Avengers: Endgame, the MCU is at a bit of a crossroads. It needs some changes. Parker Robbins’ Hood would be a great place to start with those changes.
6 Magus
While Adam Warlock is a symbol of virtue in the Marvel comics, his dark, twisted counterpart, Magus, is anything but. Magus, much like Thanos, coveted the Infinity gems (called infinity stones in the film). Perhaps the powerful objects could be brought back with this character’s debut.
The Magus' unique look and powerful abilities make him the perfect candidate to be an Avengers villain. With Adam Warlock likely appearing in the upcoming Guardians of the Galaxy Vol 3, Magus may be soon appearing as well.
5 Morgan Le Fay
A powerful witch that lived several centuries ago, Morgan Le Fay has consistently proven herself to be one of the Avenger's most problematic enemies. Scarlet Witch sort-of used magic-like powers, but other than that, the MCU’s Avengers have never faced off with a powerful magic-user.
Bringing Morgan Le Fay into the picture would be an amazing choice. The Avengers in the MCU so far have only had to face off with physical threats. A magical one would make for a great change of pace.
4 High Evolutionary
The High Evolutionary is known for his genetic experiments. Through some pretty advanced scientific processes, the High Evolutionary was able to fully evolve several different species in a short amount of time.
While the supervillain is rumored to be appearing in the Guardians of the Galaxy Vol. 3, those reports have yet to be confirmed. If they turn out to not be true, the Avengers series really would be better off if they utilized this character.
3 Korvac
Korvac was originally an incredibly intelligent scientist that traveled the multiverse studying powerful beings. He hoped to find a way to harness their powers in order to make Korvac a god-like being.
After discovering the ship of the world-eater Galactus, Korvac got his wish. Imbued with the incredible power cosmic, Korvac became one of the most powerful, despicable villains that the Marvel Universe has ever seen. It took both the Avenger and Guardians of the Galaxy to dispatch him when he attacked Earth for the first time.
2 Annihilus
Hailing from the Negative Zone, Annihilus is own of the most powerful galactic threats that the heroes of the Marvel universe ever had to contend with. The violin is hell-bent on traveling from his dimension to Earth for a full-on invasion attempt.
Visually, Annihilus would be a breath of fresh air when it comes to movie villains. Also, not only would he serve as a physical threat to the Avengers, but his army of cronies and drones from the Negative Zone would make for more than a competent Avengers-level threat.
1 Kang the Conqueror
Kang the Conqueror is by far the greatest Avengers villain yet to appear in a live-action movie. That likely won't be the case for long, given that recent reports suggest that the evil mastermind will be included in the MCU sequel to Ant-Man and the Wasp.
A time-traveling supervillain with access to super-advanced technology from the future, Kang has proven time and time again to be more than a match for Earth's mightiest heroes. It is only through sheer force of will and a good amount of luck that he was ever defeated.