Marvel's superheroes have become some of the most popular of all time thanks to their multimedia pursuits. These respected heroes have been fighting the good fight for decades, starring in some amazing stories that are still being mined for ideas. A great trope that Marvel has used better than just about anyone is the hero falling to evil.
When Marvel's heroes fall, they fall hard. Many times, these once heroic exemplars have actually endangered the entire world, forcing their fellow heroes to stop them. Other times, heroes have made mistakes that have almost ended everything, showing just how fraught with peril being a superhero could be.
10 Wolverine & Invisible Woman Created A Broken Parallel Reality In Age Of Ultron
Wolverine is one of the greatest heroes in the Marvel Universe and Invisible Woman has been a hero for longer than just about anyone but putting either of them in charge of a time travel mission isn't a great idea. After Ultron was able to nearly destroy humanity in Age Of Ultron, the two were sent back in time to stop Ultron from being built. As pragmatists, they decided the best ways to do that would be to kill Hank Pym.
This created an entirely new alternate reality, one that was completely broken. The two had to take another trip back in time to stop themselves in the past, with Wolverine having to kill a version of himself to keep the timeline straight.
9 The Ultimate Universe Reed Richards Became The Villainous Maker
The Ultimate Universe became a very different thing as it went on. In Ultimatum, Magneto caused a cataclysm that killed millions, including Invisible Woman. This drove Reed Richards insane and he became the Maker, a villain who used all of his intelligence to attack the remnants of his former friends.
The Maker would survive the destruction of his universe and find himself in the 616, again enacting destructive schemes that would be foiled by Sunspot's Avengers-A.I.M. The Maker has recently recreated the Ultimate Universe but that doesn't mean his threat has ended.
8 Adam Warlock Expelling His Emotions Endangered The Entire Universe
Adam Warlock gained the Infinity Gauntlet at the end of the miniseries of the same name. He did his best to become someone worthy of the power, so he expelled his positive and negative emotions, trying to make himself completely impartial. The problem came in that these emotions coalesced into beings, with his negative emotions becoming the Magus and the positive ones becoming the Goddess.
Warlock had faced the Magus before but the Goddess was completely new. Both beings ended up being very bad for the universe and the heroes of the Marvel Universe had to band together to stop them.
7 The Sentry Has Lost Control & Almost Ended The World Several Times
The Sentry is one of the most powerful beings on Earth but that comes with a massive drawback. Bob Reynolds was an addict who gained his powers while looking for drugs. His mental issues would manifest as the Void, a dangerous villain who could use all of Sentry's powers. The Void was so bad that the Sentry agreed to have all memory of himself erased from the world.
His memory would return and the Void would manifest several more times over the years. Each time would be an all hands on deck moment, with the heroes of the Marvel Universe having to band together to save the day.
6 Phoenix Became Dark Phoenix & Almost Destroyed Existence
"The Dark Phoenix Saga" is one of the greatest Marvel stories ever, seeing Jean Grey becoming Dark Phoenix and endangering the entire universe. While it was later revealed that it wasn't Jean at all but the Phoenix posing as her, Phoenix proved to be a powerful addition to the X-Men but wasn't ready for the realities of human existence.
This, combined with Mastermind's manipulations, caused Phoenix to go dark and lash out at her friends. Dark Phoenix would consume an entire star system and eventually committed suicide so as not to destroy all of existence.
5 Iron Man's Time As Director Of S.H.I.E.L.D. Was A Massive Failure That Almost Allowed The Skrulls To Conquer The World
At the end of Civil War, Iron Man was made director of S.H.I.E.L.D. and he botched it completely. Too obsessed with proving how great he was and how wrong everyone against him was, he missed the Skrulls quietly solidifying their control of S.H.I.E.L.D., the Superhero Initiative, and his own companies. His negligence allowed the Skrulls to almost conquer the world.
While the heroes were able to win the day, Iron Man's failures were compounded because it allowed Norman Osborn to take control of the US superhero apparatus, which led to the Void almost destroying the world.
4 Scarlet Witch's Reality-Altering Powers Could Have Ended Everything
Scarlet Witch's precarious mental state has led to some pretty bad places over the years. She's lost her mind on more than one occasion and while Avengers Disassembled and House Of M are the most recent, the Avengers have had to deal with her trying to destroy everything numerous times over the years.
Scarlet Witch has too much power for her own good. Combine that with her extremely stressful life, a life filled with heartache and pain, and she's a powder keg waiting for a spark. Luckily, she's been doing much better in recent years.
3 Professor Xavier's Time As Onslaught Almost Destroyed Everything He Created
Magneto's ripping out Wolverine's adamantium skeleton would have massive repercussions. Xavier mindwiped Magneto in revenge, which planted the seeds of Onslaught. Those seeds would grow in Xavier's psyche until Onslaught took complete control. Decimating the X-Men, Onslaught turned his sights on New York City, attacking the city with repurposed Sentinels.
From there, he would capture Franklin Richards to take advantage of the boy's reality altering abilities. Onslaught's attacks were devastating and it took the combined power of the Avengers, X-Men, and Fantastic Four to stop him, with the Avengers and the FF "sacrificing" themselves to keep him from destroying everything.
2 Cyclops's Fall To Dark Phoenix Started With The Best Of Intentions
Cyclops, Emma Frost, Namor, Magik, and Colossus gained the power of the Phoenix during Avengers Vs. X-Men and the whole thing started out rather well. The five of them used their powers to help the Earth but the Avengers' continued resistance caused them to take more and more drastic steps against their foes. This, combined with the years of pressure from leading the last remnants of mutantkind, drove Cyclops crazy.
Killing Professor X and draining the Phoenix power from Emma Frost, Cyclops would become Dark Phoenix. The Avengers and X-Men banded together against him, with Scarlet Witch and Hope Summers taking the Phoenix Force from him and using it to reignite the genetic fire of the mutant race.
1 Captain America's Time As Hydra Supreme Would Have Spelled Doom For The World
Because of Cosmic Cube shenanigans, Captain America became an agent of Hydra, taking control of the organization and S.H.I.E.L.D. He would engineer a conflict that allowed him to take control of the US government, driving his former friends underground to battle him. While he only succeeded in taking over the US, there's no doubt that was only the beginning.
It took everything the heroes had to defeat him and they still would have failed if the non-Hydra version of him didn't escape the Cosmic Cube. The original Cap was able to beat Hydra Supreme Cap and save the world from Hydra's future attacks.