"And then there came a day unlike any other, when Earth's Mightiest Heroes found themselves united against a common threat!" On that day, the Avengers were born, and since then, they've become one of Marvel's more iconic teams who constantly face down and battle terrifying and brutal villains.
Of course, like all villains, some Avengers villains actually end up being goofy and ridiculous baddies who aren't really worth being classified as a threat. However, despite these jokey villains, there are still quite a few who qualify as being true-blooded, deadly antagonists of the Earth's Mightiest Heroes, the Avengers.
Kree And Skrulls
Putting the Kree and the Skrulls together may not be that fair. After all, they are two formidable alien races who have come close to conquering the galaxy time again. And yet, their laughability comes from the Kree/Skrull war.
A large part of the Avengers story arcs, the Kree/Skrull war saw the Avengers right smackdab in the middle of a space scuffle that wasn't all that challenging to combat. Since then, the Kree and Skrulls have remained prominent Avengers foes, but they really don't d0 much damage to the team and perhaps even deserve some redemption.
Taskmaster
The ability to mimic and copy someone else's abilities is a pretty cool power for a villain to have. To go up against the Avengers though, even someone with those powers such as Taskmaster isn't going to succeed.
As great of a villain and character Taskmaster is, even with his abilities, trying to mimic the likes of a thunder god and a green behemoth doesn't sound all that realistic or bode that well for the skull masked baddie.
Count Nefaria
Even beings with immense power can be easily beaten in comics. Take Count Nefaria, who was a wealthy Italian aristocrat who always sought after power and utilized science to gain it.
However, no matter how many times Nefaria went up against the Avengers - either by himself or with his Lethal Legion - he always seemed to fail. Not to mention the fact that he was once beaten by Squirrel Girl over finger counting.
Mephisto
Making a single villain the sole cause of every misdeed or misfortune in a larger universe is ridiculous. And yet, in recent comics, Mephisto has slowly been made out to be that big bad for unknown reasons.
From supposedly manipulating every big Avengers event of the past, present, and future, giving Phil Coulson control over the Squadron Supreme, and messing with every hero's life as he did with Spider-Man, Mephisto's been made out to be Marvel's ultimate villain for unnecessary reasons, with this unbelievability making him a lesser villain overall.
Scarlet Witch
Truth is, Scarlet Witch is a fantastic character. One of the most powerful mutants alive, Wanda Maximoff has been a hero and a villain over the years, but too often she is relegated to being a baddie with little rhyme or reason.
There have been too many times where it seems like writers are insistent on making Wanda insane and having her either attack the Avengers or wiping out mutants with little reasoning behind these actions. At the moment, Wanda's villainous streak is overused, and it feels stale.
Red Skull
A lot of Marvel villains will typically crossover from one comic to another. While the Red Skull's not had a whole lot of appearances in Avengers comics, when he does show up, he tends to leave an impact.
Despite his hatred for Captain America and his constant failure, the Skull did once use the brain of Professor X for his own, utilizing telepathic abilites to mess with the Uncanny Avengers for mutliple comics.
Masters of Evil
When it comes to fighting a team of heroes, strength in numbers tends to do the trick. Led by the nefarious Baron Zemo, the Masters of Evil were a group of villains designed to destroy the Avengers.
Comprised of lower-level villains, including Skurge, Enchantress, and even Wonder Man before he became a hero, Zemo and his Masters of Evil were a sizable threat for the Avengers despite their failures.
The Beyonder
There seems to be a trend in comics where god-like beings insist on taking on normal, everyday heroes. Case in point, during the first Secret Wars event, an all-powerful being known as the Beyonder kidnapped the heroes and villains of earth.
With the Avengers among them, the Beyonder orchestrated a game of sorts for the heroes. Using his power as a toy, the Beyonder was a powerful foe but never seemed to achieve his full potential.
Dark Avengers
Heroes always seem to find themselves going up against dark mirror images of themselves. For years, Norman Osborn was the psychotic villain known as the Green Goblin. However, Osborn somehow became the head of HAMMER and later the twisted Dark Avengers.
Made up of Moonstone, Venom, Ares, Sentry, Daken, Bullseye, and Osborn as the Iron Patriot, the Dark Avengers were an inverse version of the Avengers who took their place during the "Dark Reign" storylines before being taken down.
Loki
It can be said that the first is always the best, and Loki can definitely be considered one of the best Avengers and Thor villains. The first-ever foe the Earths Mightiest Heroes took on, the god of Mischief was a prominent Avengers antagonist for some time.
Always working in the shadows, manipulating and pushing the Avengers to their very limits (and almost winning on several occasions), Loki is a complex and fun villain to see, no matter what form he takes.
Kang The Conqueror
Time-traveling Marvel heroes and villains always make for fascinating characters to explore in comics. Hailing from the 31st century, Kang the Conqueror is largely a Fantastic Four villain but has since left his mark on the Avengers.
Intent on conquering the present and any other time period, Kang became a serious threat during the massive comic arc known as "Kang Dynasty," where he conquered and devastated the world, making himself one of the Avenger's oldest foes.
Korvac
Micheal Korvac is probably one of Marvel's and the Avengers' strangest and most fascinating villains. A technician from another world, Korvac's lower half was grafted to a piece of tech, making him a powerful and nearly omnipotent cyborg.
Becoming a large threat during the Korvac Saga, Korvac arrived at Earth-616 and almost immediately took on the Avengers. In the years that followed, Korvac continued to be a massive threat to the Avengers and the entire world.
Ultron
One's darkest rival can sometimes be their own creation. When founding Avenger Hank Pym created the Artificial Intelligence known as Ultron, no one could've predicted that he would become one of the Avengers' darkest and most dangerous rivals.
Always five steps ahead of the Avengers and constantly putting them on edge, Ultron's managed to best and outsmart the Earth's Mightiest Heroes time and time again, even taking over the world at one point and defeating the team.
Thanos
Only a few villains have managed to truly beat or best the likes of the Avengers. Thanos, the Mad Titan, is undoubtedly the most well-known for his rampage during the "Infinity Gauntlet" storyline, where the cosmic villain wiped out half of the universe with a single snap.
In the aftermath, Thanos easily overcome the Avengers' efforts to stop him, and even without his Gauntlet, he has proven himself as a deadly and powerful foe for Earth's Mightiest Heroes.