A huge part of being a great hero is having an impressive stable of villains that challenge them.  They force our heroes to constantly rise to the occasion and find new ways to defeat whatever nefarious plans their rogues have put into place this time, and keep us as viewers on the edge of our seats as we wonder just how the hero will actually overcome the bad guys. Marvel's figured that out, and though there are critics who have issues with the way they handle their bad guys, the MCU has still delivered some of the most interesting takes on classic villains ever.

Still regardless of how anyone feels about the MCU's villains, Marvel has had to make a ton of changes in order to make some of them work. Sometimes the changes are because of the MCU's continuity being different from the comics, other times the creative team behind the scenes simply wanted to the villain to serve a different role in their films than the ones they do in the comics. Whatever the reason, sometimes these massive changes can slip by even the biggest Marvel fans. But CBR has you covered, and so here's 15 massive changes the MCU made to Marvel villains even die-hard fans didn't notice.

15 ULTRON IS A CREATION OF TONY STARK AND BRUCE BANNER

Avengers-Age-of-Ultron

Opinions on the quality of the second Avengers movie remain somewhat split, with most people criticizing it for losing the plot too frequently. Still, easily one of the best parts of the film is James Spader’s Ultron, an AI created by the combined efforts of Tony Stark and Bruce Banner that decides the best way to save the world is by wiping out the rest of humanity. Still, this is definitely not the original origin of one of the Avengers’ oldest enemies.

No, the comics initially saw the dangerous sentient robot created by the flawed genius of Hank Pym, and is based on Pym’s own brainwaves.

Of course, at the time Hank Pym didn’t exist yet in the MCU and the one we got was quite different than the one from the comics, so Ultron’s origins were tweaked to fit in with the MCU at the time.

14 BARON ZEMO IS FROM SOKOVIA

One of Captain America’s earliest foes, the title of “Baron Zemo” is actually passed down through a single family over centuries. Cap’s first run-in with one of them came in the '40s during World War II, but the most notable version is Helmut Zemo. In both cases though, Baron Zemo is responsible for the creation of various forms of the Masters of Evil, an evil version of the Avengers.

Zemo has a much less overt influence on Cap’s life in the MCU, but he still shakes the Avengers to their very core as the hidden, “true” villain of Captain America: Civil War. Rather than being a German nationalist, this version of Zemo is a survivor of the destroyed country of Sokovia, and his actions cause him to exploit as many weak points in the Avengers as he can to tear them apart.

13 EGO IS PETER QUILL'S FATHER

Ego Guardians of the Galaxy 2

Making his first full appearance in Stan Lee and Jack Kirby’s Thor #133, Jack Kirby described Ego’s formation as a giant virus that sat undisturbed for millions of years, evolving on a planet until it gained the ability to think. Freaky! But Ego’s though first appearance is as a Thor villain, it’s in the MCU’s Guardians of the Galaxy Vol. 2 that the deranged planet makes its big-screen debut, and he comes with a massive change.

The film presents Ego as the father of Chris Pratt’s Star-Lord, a man who came down from the stars and fell in love with an Earth woman.

Of course, comic book Peter Quill has a completely different father: J’son, King of Spartoi. How he meets Quill’s mother is much the same, but one supposes they didn’t use him ‘cause it isn’t nearly as attention-grabbing as saying a superhero’s father is an entire planet!

12 OBADIAH STANE IS STARK'S FRIEND

Obadiah Stane Jeff Bridges

As the very first villain of Marvel’s MCU, Obadiah Stane kind of sets the stage for this entire article. In the very first Iron Man, he starts out as Tony’s mentor and confidant, a business partner to his father Howard that stayed on at the company for years until he decided he wanted to control Stark Industries for himself and has Tony nearly killed by a terrorist organization known as the Ten Rings.

But in the comics, makes Stane a much more formidable opponent. He runs his own business -- Stane International -- and eventually goes after Stark Industries to become the number one munitions manufacturer. He does everything from steal Stark’s company to manipulating him into giving into his alcoholism, eventually leaving him as a homeless man wandering the streets.

11 THE VULTURE IS A FAMILY MAN

“You either die a hero, or you live long enough to see yourself become the villain.” In the most meta of ways, those words serve as an eerie prophecy for the fate of Michael Keaton. Starring as Batman nearly 30 years prior in a film that arguably started the superhero craze, his return to the world of superheroes sees him shift to the other side as one of the best parts of an already great Spider-Man film as Adrian Toomes, the Vulture.

But the Vulture that Keaton plays is staunchly different from the one fans had grown used to in comics and cartoons alike.

Once a scientist driven to crime over stolen inventions, Toomes is now a much more relatable character: a salvager, driven to crime in order to protect his business and his family.

10 BARON MORDO STARTS AS A GOOD GUY

dr-strange-mordo

This is one of the crazier changes because it’s almost like an inversion of what the source material intended. Much like the film, in the comics Mordo is a student of the Ancient One, but from the very beginning he plots to destroy the sorcerer. Unlike Stephen Strange, from the very beginning Mordo is more willing to take advantage of darker arts and spells in order to become more powerful.

By comparison, the Mordo from the Dr. Strange movie starts out as a loyal student of the Ancient One and even a close friend of Stephen Strange. But he’s far more by the book, believing vehemently that the rules exist to be followed and anyone who breaks them disrupts the natural order. His unwillingness to adapt according to different situations eventually drives him mad, leading him to decide that magic itself is evil, setting him on the path of villainy.

9 MALEKITH IS FAR MORE SANE

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Thor: The Dark World is a rare blemish on the MCU. The universe is no stranger to less than stellar movies, but despite this film’s star-studded cast Dark World feels…outright boring. A lot of the fault doubtlessly lies with Malekith, a character that’s quite the deviation from his comic book self. The original Malekith is something of an Asgardian Joker that belongs to the world of Dark Elves, a place that feels like the source of every twisted fairy tale at once.

He’s a creature of malice and chaos, and encourages (and often causes) war because he feels it gives his life meaning.

By comparison, Christopher Eccleston’s character is a much calmer, more measured character that’s seeking revenge due to his loss in battle against Odin, and possesses a desire to restore the Dark Elves. It makes him more relatable, but not really more interesting.

8 JUSTIN HAMMER IS COMIC RELIEF

Justin Hammer in the MCU

Whether you thought Iron Man 2 was a good film or not, one thing’s for certain: Justin Hammer is just not an impressive villain. Though Sam Rockwell plays the part well enough, the character is never meant to be the true antagonist to Stark and plays backseat to Whiplash. The film leaves Hammer in charge of his own company, but de-ages him until he’s about Tony Stark’s age and turns him into something of a bungling idiot who’s inventions don’t work nearly as well as his rival Tony Stark’s.

Though it can be argued just how effective Justin Hammer runs his company in the comics, what’s not really up for debate was how dangerous he was. There, he not only managed to deduce Tony Stark’s secret identity, but successfully hack into Stark’s systems and cause him to kill a foreign dignitary. Scary stuff.

7 DARREN CROSS WASN'T ORIGINALLY YELLOWJACKET

Darren Cross Yellowjacket

This one’s more of the movies influencing the comic books. In the 2015 film Ant-Man, viewers are introduced to Darren Cross, a former protégé of Hank Pym that takes over Hank’s company Pym Technologies to gain control over Pym’s secret Ant-Man shrinking tech. Eventually he figures out a form of the shrinking powers and creates his own armor, the Yellowjacket.

The comics naturally tell a different story (or he wouldn’t be on here), with him having no connection to Yellowjacket at all.

Originally, Darren Cross was a CEO with a heart problem, and his pacemaker altered his physiology in a way that gave him superpowers. Though using the powers burned out his heart, Cross underwent multiple transplants by kidnapping “donors” from off the street. And while the comics would eventually see him take the Yellowjacket identity for his own, that wouldn’t happen until after the film became a smash hit.

6 TURK BARRETT IS MORE THAN OBSCURE TRIVIA

turk barrett

By this point, everyone who watches Marvel’s Netflix offerings recognizes Turk Barrett. Played by Mark Acheson, he’s something of a recurring character that’s managed to appear in Daredevil, Luke Cage, The Defenders, and The Punisher. He often very narrowly avoids being killed by the bad guys, and finds himself being beaten up by the good guys for his ne’er-do-well ways. It’s a rough job being comic relief, but someone’s gotta do it.

But it’s actually quite the step up from Turk Barrett’s life in the comics, where he’s barely ever mentioned or seen at all. He’s stolen the costumes and armors of a few D-List supervillains, but even then he’s not really more than a piece of comics trivia. This is a massive change from the Netflix world, where his actions (intentional or not) have kickstarted gang wars.

5 LOKI BECOMES AN ANTI-HERO

loki in the avengers

Tom Hiddleston’s Loki is the one villain that dodges all the complaints people tend to have about Marvel villains. Though the fact that he wasn’t unceremoniously killed off at the end of the first Thor helps, a lot of it comes down to their willingness to make him into a three-dimensional character.

He isn’t consistently evil, and can often be a help to his brother just as much as he is a hindrance.

Still, that’s a far cry from the villains’ earliest appearances in the comics. There, Loki is a god whose plans run far more evil, and although in both the films and the comics his actions bring about the creation of the Avengers, in the comics he plays the role of a villain much more often, wreaking havoc in repeated attempts to conquer Midgard.

4 ABOMINATION'S NOT A SPY

Abomination Lamest MCU villains

People often forget that the second Hulk film in 2008, The Incredible Hulk, is as much a part of the Marvel Cinematic Universe as Iron Man, Captain America, or anything else. But no, it launched the same year as Iron Man and even featured Robert Downey Jr. in one of the famous after-credit scenes that the MCU has popularized.

The film featured Hulk rival The Abomination as its primary villain, and the gist of the character remains the same: he’s still a larger, more mindless version of the Hulk with strength that surpasses Ol’ Green Jeans, but there’s one key difference. In the MCU, Emil Blonsky is a member of the United Kingdom’s Royal Marine Commandos that just happens to be born in Russia, while the original version is actually a KGB agent who works in America as a double-agent!

3 BLACK MARIAH IS A MAJOR PLAYER

Mariah Dillard

While Cottonmouth and Diamondback gave our bulletproof hero the most trouble, Alfre Woodard’s Mariah Dillard wound up being the unexpected “true” villain of Luke Cage.

But the former politician turned shady nightclub owner and ruler of Harlem’s underworld certainly doesn’t come from very threatening origins in the comics.

The character known as “Black Mariah” in the source material is a much more cartoonish villain, with her name coming from an ambulance that picked up the recently deceased around New York City. Mariah steals the ambulance and uses it as a way to steal valuables of people the ambulance would pick up. And while she would eventually grow into a fearsome drug dealer, she’s got nothing on the woman who went from glad handing supporters to murdering her cousin in cold blood.

2 GRANDMASTER: RULER OF SAKAAR?

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Perhaps one of director Taika Waititi’s best choices for Thor: Ragnarok was picking the eclectic Jeff Goldblum to play as The Grandmaster. Though he looks distinctly less alien thanks to a lack of blue skin, that’s not what lands him on this list as it’s too obvious a change.

No, what places Grandmaster on this list is that in the film, he’s somehow become the defacto ruler of Sakaar, the alien planet that Thor lands on after being thrown out of the Bifrost on his way back to Asgard. Long-time Hulk fans will remember Sakaar as the planet where Hulk landed after the rocket he was trapped in by the Illuminati was knocked off-course. There’s still a shout out to this, with Grandmaster using Hulk as a champion gladiator for his own amusement, but it isn’t quite the same.

1 HELA IS THOR'S SISTER

thor ragnarok hela kills asgardians

Cate Blanchett played a delightfully terrifying villain in Thor: Ragnarok, not only easily laying out the God of Thunder, but destroying his trusty hammer Mjolnir and conquering the land of Asgard before deciding to move on with the purpose of taking over all of the realms, becoming the ruler of all the lands that her father Odin chose to leave free. But Thor: Ragnarok makes a very central change to the myth and background of the goddess of death.

The film made her Odin’s daughter and Thor and Loki’s long lost sister.

Originally she has no such connection to Odin or Thor, and is the daughter of a Loki from a previous version of Asgard prior to Ragnarok. Quite the significant change, but it’s hard to argue that the story doesn’t have a much stronger emotional connection as a result.