This year marks the 10th anniversary of the Marvel Cinematic Universe, and the franchise is showing no signs of stopping. The MCU's success has often been the topic of discussion among comic book fandoms. While there are many factors at play, one of the most important reasons has been its successful treatment of a shared universe model. Due to its overarching storyline, the saga adopted a unique episodic approach that's carried over through each installment. Every single film -- no matter if it's a standalone adventure or an epic team-up -- builds from what came before it, and in some cases, lays the groundwork for what will come later. It's an engaging formula that keeps audiences interested for the next chapter in the saga.
It can also be the cause for some frustration, however, because the ongoing narrative opens the door for some nail-biting mysteries. With 18 movies that have explored dozens of different characters, the franchise has accumulated its fair share of question marks. Those range from the mundane, to pivotal unexplored plot points that would represent titanic shifts for the series as a whole. With that in mind, let's take a look at 15 burning MCU mysteries that fans would love to have to have answered:
15 WHAT HAPPENED IN BUDAPEST?
Little was known about Black Widow and Hawkeye when The Avengers came out, but the film dropped a few hints about their backstory. One in particular has been driving fans mad for awhile. During the Chitauri invasion, Hawkeye and Widow were having a hard time holding back the alien forces. To lighten up the mood, Natasha told Clint that their situation was similar to a mission they'd carried out in Budapest. Clint responded with an unenthusiastic "You and I remember Budapest very differently."
The fact that Widow was comparing a full-on alien invasion to a conflict in Budapest piqued viewers' interest, and people began to wonder what transpired during that mission. As exciting as knowing what went down in Budapest would be, though, Widow's remark was ultimately a throwaway line meant for comedic purposes, and will probably never be explored further.
14 HOW DID THE ANT-MAN SUIT AFFECT HANK PYM?
Hank Pym and Scott Lang's mentor-mentee dynamic in Ant-Man led to an intriguing mystery. At one point, Scott asked Hank why he didn't come out of superhero retirement to stop Darren Cross. Pym revealed that he physically couldn't do it, as his suit took a toll on him. Curiously, the only side effect from wearing the suit established in the film was a chemical imbalance from not using the helmet when shrinking.
Given that, Pym may have been hinting at other, unknown side effects that stem from longtime use of the suit. Unfortunately, we'll probably not learn what those are, at least not until Ant-Man & The Wasp gets released. Even then, however, it's not a sure thing, given how the Ant-Man suit has gone through many modifications since its first appearance, and any kinks will have most likely already been worked out.
13 WHATEVER HAPPENED TO THE ABOMINATION?
He may only have one film appearance under his belt, but the Abomination is one of the most talked-about baddies in the MCU. Following his defeat in The Incredible Hulk, Emil Blonsky's fate was kept a secret for years. That changed in 2011, when the MCU One-Shot "The Consultant" revealed that the World Security Council wanted Blonsky released from custody to join the Avengers.
Then, in Agents of S.H.I.E.L.D., Coulson off-handedly remarked that Abomination was being held in a cryo-cell in Alaska. S.H.I.E.L.D. crumbled shortly after that episode, though, and Abomination's whereabouts became a big question mark once again. Unfortunately, there haven't been any mentions of the baddie in either the TV or big screen side of the MCU ever since. Given all the films Marvel Studios is currently working on that don't involve the Hulk, it's unlikely that we'll ever get to know what happened to Blonsky.
12 BUCKY AND BLACK PANTHER'S STRANGE CONNECTION
Despite his prominent role in Civil War, T'Challa left audiences with quite a few question marks related to his origin and background. One of the most interesting questions arose during a pivotal action scene in the film. Shortly after being captured by the police, a mind-controlled Bucky broke out of his cell, and T'Challa tried to stop him. During their scuffle, T'Challa's ring got near Bucky's arm, and the two metals started emitting a mysterious vibration.
The metals' reaction puzzled viewers, and it even caught T'Challa off-guard. Their interaction was quickly brushed over, though, and we were left to wonder what had happened. Fortunately, Wakanda and its science will get the spotlight in Black Panther and Infinity War, so an explanation for their encounter could be right around the corner.
11 DOES HOPE VAN DYNE HAVE POWERS?
Ant-Man delved deep into the Pym family history, but left some mysteries unsolved. One of the most significant ones came courtesy of Hope van Dyne. To prepare for their Pym Technologies heist, Hope and Hank Pym started training Scott Lang to master the Ant-Man suit. The hero found trouble when it came to controlling ants, though, and Hope took it upon herself to communicate with the insects.
Hope displayed a mastery over her father's technology, but quickly lost control of herself. Hundreds of ants began to surface and the lights in the room started to flicker before Hank stopped his daughter. The film didn't delve into what exactly happened, but it was seemingly implied that Hope had some sort of super human abilities. Hopefully, this mystery will be answered in Ant-Man & The Wasp.
10 HOW DOES BLACK WIDOW KNOW BUCKY BARNES?
Natasha Romanoff is one of the most enigmatic characters in the MCU, but Civil War offered an intriguing glimpse into her backstory. After being released from his containment unit by Zemo, the Winter Soldier went on a rampage inside a government facility. Black Widow went to face him, but Bucky got the upper hand and started choking her. In response, Romanoff desperately asked him if he recognized her.
Widow's question came as a surprise, as it implied a shared history with the Winter Soldier. Unfortunately, the film quickly moved on from that, and we were left to wonder what she meant. Considering how, in the MCU, both characters worked for Russian organizations, it's not far-fetched to assume they met at some point in the past. It's unclear when this mystery will be unravelled, but who knows? Perhaps we'll get an explanation in the planned Black Widow movie.
9 HOW DID TONY AND PEPPER GET BACK TOGETHER?
Tony Stark and Pepper Potts' romance has been a pivotal part of the MCU for years, but their relationship isn't very stable. Things seemed to be going great for the couple by the end of Iron Man 3, but in Civil War, Tony revealed that he and Pepper had called it quits. Their break-up seemed to be anything but friendly, as Stark couldn't help but frown whenever her name was brought up. Surprisingly, that all changed in Spider-Man: Homecoming.
During the film's final scene, it was revealed that Tony and Pepper were back together. It was great to see them as a couple again, but the scene made us wonder what motivated them to continue their romance, especially after such a bitter separation. Set pictures from Avengers 4 have shown that Tony and Pepper are still an item, so we'll probably not get an explanation for their reconciliation any time soon.
8 HOW DID UNCLE BEN DIE?
Spider-Man: Homecoming largely stirred away from Spidey's origin story, but it did include a subtle nod to Uncle Ben's death. While strolling through New York City, Peter told Ned he couldn't reveal his super heroic efforts to Aunt May due to everything she had been through. This quick exchange interested fans, as it raised the question of how Uncle Ben met his maker.
There have been various versions of Uncle Ben's death over the years, and in most cases, his demise becomes one of Peter's greatest burdens. The MCU Spider-Man is the most hopeful live-action version of the web-slinger yet, so it would be interesting to see how Uncle Ben died to get a better sense of how the event impacted Peter. Unfortunately, given Marvel and Sony's (understandable) determination to not explore what's come before, it's unlikely we'll ever get to know how Ben Parker met his end.
7 WHY DID ODIN CREATE A FAKE INFINITY GAUNTLET?
Back in 2011, comic book fans were pleasantly surprised to see the Infinity Gauntlet stashed away in Odin's weapons room during a scene in Thor. As the franchise progressed and the Infinity Gauntlet storyline developed, however, the gauntlet's cameo started to feel more and more like a glaring continuity issue. Marvel decided to fix that in Thor: Ragnarok, by having Hela walk past the artifact and dismiss it as a fake.
That moment made fans wonder: why would Odin have a fake Infinity Gauntlet in his personal vault? Ragnarok established Odin as a power-hungry king, but that still didn't explain what motivated him to build a replica of one of the most powerful weapons in the galaxy and stash it away in a secret room. Sadly, with Asgard destroyed and Thanos in possession of the real gauntlet, we probably shouldn't expect an answer to this mystery.
6 HOW DID NICK FURY LOSE HIS EYE?
With seven film appearances under his belt, Nick Fury has become an integral part of the MCU. Still, the man lives up to his super spy reputation, because so far, he's managed to remain a riddle wrapped in a mystery inside an enigma. One of the character's biggest question marks is his missing left eye. Fans got a hint of what happened to him in The Winter Solider, when Fury stated that trusting another person cost him an eye.
Understandably, Fury's hint wasn't enough, and audiences were left to come up with their own theories to explain the character's injury. Fortunately, we'll get to discover what happened to him in Captain Marvel. The film will feature a younger version of the super spy, and will explain how he lost his eye. Admittedly, the movie is still ways away, but at least we know an explanation is on the way.
5 WHO BEHEADED THE CELESTIAL THAT BECAME KNOWHERE?
Guardians of the Galaxy did a lot for the MCU. It presented a likable group of rag-tags to audiences, introduced the universe's cosmic corner, and inadvertently created one of the franchise's most intriguing mysteries. Halfway through the movie, the Guardians traveled to a mining colony called "Knowhere." As Gamora explained, the colony was built inside the severed head of a Celestial, an ancient being of seemingly unlimited power.
Gamora's explanation made several fans curious about the alien's beheading. After all, what kind of being is powerful enough to take down and dismember a Celestial? Unfortunately, this is one bit of trivia that will probably never get answered, as Knowhere's backstory is a mystery even in the comics. However, it's still exciting to have a hint of the god-like individuals floating around the MCU.
4 WILL THE REAL MANDARIN EVER SHOW UP?
Iron Man 3 delivered quite a shocker with the revelation that Ben Kingsley's Mandarin wasn't the criminal mastermind the world thought him to be. In reality, he was an actor named Trevor Slattery hired by Aldrich Killian (who identified himself as the real Mandarin) to give authorities a face to go after. Unsurprisingly, Marvel faced an extreme amount of backlash for that plot twist, and the studio was forced to retcon it through the 2013 One-Shot All Hail The King.
The short revealed that the Mandarin, leader of the Ten Rings, was real. The retcon prompted fans to wonder whether the elusive character would make an appearance in the franchise. Sadly, we probably shouldn't hold our breath for such a thing. The One-Shot happened mainly to appease angry comic book faithfuls, and with no Iron Man 4 in the horizon, the Mandarin will probably stay hidden in the shadows.
3 WHY DID TONY STARK COME OUT OF RETIREMENT?
Iron Man 3 marked a complete status quo shift for Tony Stark. Near the end of the film, the billionaire decided to destroy all of his suits in order to dedicate himself to Pepper. It was a big step for the character, and it signaled a significant moment of growth for him. Surprisingly, though, by the time Age of Ultron came around, Tony was back as Iron Man, mopping up Hydra alongside the rest of the Avengers.
Seeing ol' Shell Head back in action was great, but fans were left wondering what had motivated Stark to return to his superhero lifestyle. The answer is somewhat given in Civil War, as Tony stated that he simply didn't want to stop being Iron Man. While it was a solid explanation, it would have been good to see what exactly prompted Tony to return to his high-tech suit.
2 WHERE'S THE LEADER NOW?
Yet another unresolved villain from The Incredible Hulk. Near the end of the film, Samuel Sterns -- the scientist who tried to cure Bruce Banner from the Hulk -- was attacked by the Abomination. The attack resulted in several drops of Banner's blood dripping into an open wound in Sterns' forehead. Immediately after coming into contact with the blood, the scientist's head started to grow.
The scene signaled Sterns' transformation into The Leader, one of the Jade Giant's most dangerous adversaries. Fans got incredibly excited by the tease, and immediately started speculating about his role in the MCU moving forward. Sadly, it's now been ten years since The Incredible Hulk hit theaters, and there's been no sign of the character in the franchise. With no Hulk solo film in the horizon, we'll probably never know what happened to the would-be villain.
1 WHAT DID LOKI WANT WITH LORELEI?
Nowadays, Agents of S.H.I.E.L.D. rarely crossovers with the big screen side of the MCU, but back in season one, the show set up an fascinating storyline for the films. In the episode "Yes Men," Lady Sif arrived on Earth with the mission to apprehend Lorelei, an Asgardian escapee and powerful sorceress. Sif captured her target with the help of Coulson, but before going back to Asgard, the warrior revealed something about her mission: Odin ordered Lorelei to be returned to Asgard alive.
At the time, Loki was posing as the Allfather, meaning Sif's trip was actually commissioned by the God of Mischief. The reason behind this move was intriguing, but to the dismay of fans, the plot point didn't lead anywhere. Given Marvel TV and Marvel Studios' strained relationship, we probably shouldn't expect storylines established in the TV side of things to affect the franchise's big screen corner.