1. Thanos (Avengers: Infinity War, Avengers: Endgame)
Ultron is among the Avengers' most powerful villains in the comics – and one of the few Marvel villains to be exclusive to the group rather than an individual hero. However, the MCU did him dirty by reducing him to only one movie, Avengers: Age of Ultron, and portraying him as a pushover.
Thanos has long been one of Marvel's greatest villains, and he has an interesting history.
The Avengers' first-ever adversary is the Asgardian god of mischief, Loki, who attempts to rule the Earth, aided by an invading Chitauri army. Loki was, in fact, working at the behest of the Mad Titan, Thanos, who would formulate new plans in the wake of Loki's defeat.
Even without the Infinity Gauntlet, Thanos has proven himself to be a hugely powerful threat, often taking on entire teams of Avengers at once. However, it is with the Infinity Gauntlet that he can most consistently defeat the Avengers.
Mandarin - The archenemy of Iron Man, the Mandarin is a Chinese nobleman, scientist and former diplomat turned criminal mastermind.
That villain is, of course, Kang the Conqueror, who's set to be the Avengers' next opponent in the upcoming Avengers: The Kang Dynasty. And while Thanos is certainly a hard act to follow, Kang may be a far greater threat than the Mad Titan ever was.
While Thanos is an Eternal and has the standard powers of super-strength, agility, regeneration, immortality, and more, Adam Warlock takes the upper hand. He can be killed, but he resurrects to be stronger every time.
Hercules / Zeus
In fact, he is considered by many authorities to be the physically strongest character Marvel has ever created.
Loki – Thor's archenemy and adoptive brother. The son of Laufey, ruler of the Frost Giants of Jotunheim, one of the "Nine Worlds" of the Asgardian cosmology. He is a master of spellcasting and trickery. Lorelei – The sister of Amora the Enchantress, who possesses some skills in Asgardian magic and seduction.
Tony Stark is the smartest of them all, having been responsible for some of the most incredible inventions to have ever graced the Marvel universe, including the Arc Reactor and one of the most sophisticated artificial intelligence systems known to man.
Thanos – Avengers: Infinity War and Avengers: Endgame
So did Marvel succeed? Well, kinda. In terms of impact on the MCU characters, yes, Thanos is the baddest of them all. He kills half the universe!
Thanos. Certainly, the most well-known of the major antagonists in the Marvel Universe. In the comic books, Thanos was driven by a desire to impress Death herself. Thanos has become an icon in more recent years because of his portrayal in the Marvel Cinematic Universe.
Developing powers like his fellow Oans, Krona is more than powerful to defeat Thanos. Beyond his vast energy powers, Krona has mighty mental abilities that would allow him to defeat Thanos. The Mad Titan has defenses against mental attacks, but not at the level that Krona is capable of.
Loki's tricks work against many but not against Thanos. In a battle of wills, Thanos is always going to win against Loki. In a physical battle, Loki can't stand up to Thanos either. Try as he might, Loki just can't stand up to Thanos's power.
Thor is repeatedly vanquished by the 5 new Phoenix hosts over the course of 12 issues: Colossus, Namor, Cyclops, Magik, and Emma Frost. Colossus even manages to knock Mjolnir out of Thor's hands at one point, demonstrating the strength of Phoenix and why it should not be trifled with.
Kang has arrived. At Comic-Con 2022, Marvel Studios' Kevin Feige made official what many fans had been theorizing for some time: Kang the Conqueror is the MCU's next Thanos-like villain.
Ant-Man and The Wasp: Quantumania director Peyton Reed hints at Jonathan Majors' Kang the Conqueror as a bigger villain than Thanos.
Apocalypse. En Sabah Nur AKA Apocalypse is the oldest of all the mutants in the Marvel universe. He possesses a myriad of powers, both physical and mental, which often makes people forget that he is incredibly powerful when it comes to his basic physical strength. In fact, he is proven to be much stronger than the Hulk ...
The Norman version of the Green Goblin is usually regarded as Spider-Man's archenemy. The second Goblin, Harry Osborn, is Norman's son and Peter Parker's best friend. He has the same powers as his father.
Tony Stark's best friend, James Rhodes, is one of the few to wear the Iron Man armor, other than Tony Stark himself.
No one in the Marvel Universe dislikes Iron Man more than Captain Marvel does. That includes the Mandarin, Whiplash and Justin Hammer.
Thor: The God of Thunder almost killed Thanos in Avengers: Infinity War. He really would have taken down the Mad Titan there and then if not for his wish to see Thanos realise the error of his ways. As Thanos said, he should have gone for the head. We think if Thor got another chance, he would not miss.