Although it was recently confirmed that Guardians of the Galaxy Vol. 3 will include Adam Warlock, it's unknown whether the cosmic hero will take on a hero or villain role. However, the fact that his cocoon was revealed by the Sovereign High Priestess Ayesha in the previous movie could suggest that she'll be the one controlling him as an antagonist to the Guardians.
If that is the case, it continues an MCU trend of intelligent villains that orchestrate their plans in the background rather than always taking a direct role in things. Of course, the MCU isn't the only source of clever superhero movie villains, and so the movie fans of Ranker each voted for who they felt was the smartest antagonists from all that's out there.
Note: Ranker lists are live and continue to accrue votes, so some rankings may have changed after this publishing.
Green Goblin (Spider-Man)
The Green Goblin is something of a mad scientist in the way he willingly experiments on himself with supposedly body-enhancing chemicals that ultimately drive him to murderous rage. Yet there's no doubting the skills that made him renowned around the world as well as a multi-millionaire in Sam Raimi's Spider-Man.
What makes the Green Goblin stand out is the way he manages to use his intelligence to make himself Spider-man's greatest threat, including working out the hero's identity from seeing a wound and then immediately working out how he can use this against him. Even though his plans ultimately backfire, his place as the renowned villain of a popular movie means he was always likely to be a strong choice.
Ultron (Avengers: Age Of Ultron)
Ultron always had an advantage when it comes to the intelligence category thanks to being an all-knowing AI, as well as the creation of two already formidable minds in the form of Tony Stark and Bruce Banner. However, thanks to the origins of the code they used in the Mind Stone of Loki's Scepter, this impressive intelligence turns into evil intent very quickly.
Although his plan to wipe out all life on Earth makes him an antagonist that's hard to empathize with, the way he quickly manages to create his Doomsday Trigger and overpower the Avengers is an impressive testament to his mind. Avengers: Age of Ultron isn't considered one of the best MCU movies but its villain stood out for a lot of fans on Ranker.
Doctor Doom (Fantastic Four)
One of the most iconic Marvel villains outside of the MCU, Doctor Doom has been one of the best Fantastic Four comic characters since his debut. Although Fantastic Four was a film series that divided opinion, one of the best parts for a lot of fans was seeing the schemes of one of the smartest Marvel villains.
As well as being the sharp CEO of Von Doom industries in Fantastic Four, Doctor Doom was smart enough to take a chance on Reed Richards and his research that culminated in their superpowers. He also identifies that his best way to take down the group is to drive a wedge between Ben and Reed and, though the movie didn't impress viewers much, Doom was certainly able to.
Doctor Octopus (Spider-Man 2)
Portrayed by Alfred Molina in Spider-Man 2 and again more recently in Spider-Man: No Way Home, Doctor Octopus is a fan-favorite character from Marvel and it's easy to see why he garnered a lot of votes on Ranker. His ingenuity is self-evident in the giant robotic tentacle limbs he built for himself that are powered by an AI that eventually takes him over.
Before then, however, Otto provides a mentor for Peter Parker's own scientific aspirations and it's easy to see why Peter looks up to him. As a supervillain, the only person who could really stop Doctor Octopus was himself, and ultimately, his decision to overrule the tentacles with his mind and sacrifice himself to destroy them just demonstrates the strength of his intellect.
Magneto (X-Men)
Whether portrayed by Sir Ian McKellen or Michael Fassbender, Magneto is a powerful presence in any movie he happens to be in, beginning with the first X-Men movie. There aren't many villains who could outwit the mind of Professor X and the fact that Magneto is able to go toe-to-toe with the other man is already evidenced enough by his intelligence.
As well as using his powers and his mask to ensure he's almost impossible for the X-Men to take down, Magneto is also smart enough to take advantage of his charisma to use the powers of his followers to their fullest extent. Even when using his intelligence for the most sinister of purposes, Magneto is a compelling antagonist that fans love to watch.
Lex Luthor (Batman V. Superman: Dawn Of Justice)
There's only one villain capable of concocting an absurdly complex plan to set the world's greatest heroes against each other and of course, that's Lex Luthor. Though Jesse Eisenberg wasn't everyone's favorite iteration of Lex Luthor, there's no doubt it was one of the most serious and most intelligent versions of the iconic villain.
In Batman V. Superman: Dawn of Justice, the Lex Luthor the audience sees is a young ingenious entrepreneur obsessed with bringing down Superman. Even when his plan fails at the last second, the fact that Luthor had even thought of a backup plan helps set him apart from some of the more cartoonish portrayals of the villain that had come before and established him as a more intelligent villain in the eyes of fans.
Loki (Thor: The Dark World)
Although it's considered a terrible sequel that surprisingly didn't kill the franchise, Thor: The Dark World did give audiences a chance to see more of the enigmatic brother of Thor. Of course, Loki had already been established as a smart villain, albeit one who's not always fully in control of his own schemes.
Perhaps the best way Loki shows off his intelligence in the MCU movies is through his uncanny ability to get under the skin of everyone around him, friend or foe. He displays a knack for a deception that most villains could only dream of, even convincing Thor of his death in Dark World. With his own Disney+ show, Loki consolidated his place as one of the most prominent and complex villains.
Helmut Zemo (Captain America: Civil War)
Helmut Zemo may not be the most popular antagonist in the MCU but, in some ways, he does manage to appear as one of the smartest. Whereas most can't help but hog the limelight, Zemo mostly works in the shadows, putting his strategic mind to use without ever putting himself at risk.
Of course, his most impressive feat is driving a wedge between the Avengers in Captain America: Civil War. Though it's easy to mock the plan as overly convoluted, the fact it succeeded goes to show that Zemo is never a man to be underestimated, especially when it comes to his intelligence, and many fans on Ranker seemed to agree.
Ozymandias (Watchmen)
It takes a lot to stand out as an intelligent villain against the might of the Marvel and DC universes and the fact Ozymandias holds such a high position is a testament to how highly fans rate the character's brains. While any villain can create destruction, Ozymandias does something even more impressive.
In Zack Snyder's Watchmen, he orchestrates not just a huge amount of destruction but also a plot to pull the wool over the eyes of the entire world and convince them to unite against an innocent Doctor Manhattan. Along with his photographic memory, his incredible inventions, and his arrogant persona, it's easy to see how he made such a big impression on fans.
The Joker (The Dark Knight)
There have been several incredible versions of the iconic villain, not least Joaquin Phoenix's interpretation which will appear again in Joker 2, but Heath Ledger shows the villain at his ingenious best. In The Dark Knight, he manages to be the greatest match for Batman that Nolan's movies produced.
Though his actions appear erratic and nonsensical sometimes, there's a lot of thought and planning that goes into them. Even when he gets captured apparently against his will, it turns out to be part of his plot. An incredible villain but not a stupid one, the Joker's complex schemes won over the movie fans of Ranker.