The Marvel Cinematic Universe has developed a reputation for foreshadowing huge revelations in little moments multiple films and years before they're revealed, so it's no surprise that fans pour over every minute of the MCU to try to predict where it will go next. Sometimes the theories are really, really out there, but other times they've been proven right.

RELATED: 15 Marvel Events You Will Never See On-Screen.

Kevin Feige has stated that Marvel Studios has plans for more superhero movies through at least 2020, so what secrets are right in front of us? How much of the future of the MCU have we already seen hinted at, and what hidden meanings have we missed? Some of them might just blow your mind. Here are the top 15 MCU fan theories that will freak you out!

SPOILER ALERT: The following article contains spoilers for several MCU films including "Guardians Of The Galaxy Vol. 2"

15 OBADIAH STANE WAS HYDRA

Jeff Bridges as Obadiah Stane looking rather sinister in Iron Man

HYDRA's existence in the modern age wasn't revealed until "Captain America: The Winter Soldier," but this theory suggests that they've actually shown up in the MCU as far back as its first film in "Iron Man." The theory is that Obadiah Stane came to Stark Industries to take control of the company and use it to shape the world in HYDRA's image. He quickly rises to second-in-command and is poised to take over after HYDRA arranges for Bucky to kill Howard Stark, if not for Tony's intervention. The first thing we learn in "Iron Man" is that Stane was acting as interim CEO for the company until Tony returned to take over.

Since Tony is a genius weapons engineer who doesn't get involved with politics, HYDRA allows him to continue to revolutionize the weapons industry. When his playboy ways start to worry HYDRA, Stane arranges for him to be killed after completing their best weapon yet: the Jericho missile. "Weapons that will help steer the world back on course" and "put the balance of power in our hands. The right hands!" All that sounds kind of off for a guy who's selling directly to terrorists, unless he's intentionally destabilizing the world so that a bigger organization can take control is the goal.

14 HYDRA WAS BEHIND ASSEMBLING THE AVENGERS

HYDRA-AVENGERS

In "Captain America: The Winter Soldier," we learn that HYDRA has been tracking potentially powered people for years with Project Insight, even having Stephen Strange on their radar well before he traveled to Karmar-Taj and learned about the mystic arts. They had already tried to take out Captain America in the 1950s, and, if our last theory is correct, then they tried to take out Iron Man too. With even more heroes on the radar, HYDRA decided to take out all their threats at once, using S.H.I.E.L.D. to assemble the Avengers.

In the Marvel One-Shot, "The Consultant" we see Jasper Sitwell (now known to be a HYDRA double agent) further push the Avengers to assemble. After the events of "Thor," HYDRA worked with Loki to arrange the Chitauri invasion in New York and sent the Avengers in, only to launch a missile straight toward them. Then, even though Nick Fury ordered against it, a rogue S.H.I.E.L.D. (read: HYDRA agent) carried the missile in anyway with a jet.

13 LOKI LOST AGAINST THE AVENGERS ON PURPOSE

Tom-Hiddleston-Loki-Captured

Loki is the god of mischief. He's a manipulator, a schemer, a plans-within-plans kind of guy, so why is everything he does in "The Avengers" so straightforward and kind of... dumb? He first gets captured when he stands in front of a crowd of people and makes a huge scene. Then with no fight at all, he accepts capture and is brought aboard the helicarrier. The Avengers realize that he wanted to get captured to unleash The Hulk, which he only did to bring The Avengers together.

Loki made it clear in "Thor" that he has no interest in Earth. He wants to rule Asgard, so why bother enslaving and manipulating people on Earth in the first place? He uses the scepter to manipulate Selvig into putting a failsafe in the portal device, so The Avengers can close the portal, get the tesseract and send it back to Asgard with Thor and Loki in tow. With yet another infinity stone in Asgard, plus the gauntlet itself as revealed in "Thor," Loki is in the perfect position to take Asgard, and Thanos gets the gauntlet (as we see at the end of "Avengers: Age of Ultron") so he can take Earth.

12 THE RED SKULL IS STILL ALIVE

Red-Skull-Hugo-Weaving

In the comics, the Red Skull is one of the best Marvel villains of all time, so when he met his apparent end in "Captain America: The First Avenger," fans were understandably disappointed. Not every Marvel villain is a winner, so why kill off one of your heaviest hitters in his first film? Unless they didn't. The last time we see Red Skull, he's holding the Tesseract as it seemingly dissolves him, sending a bright blue beam into the sky, opening a portal and sucking him up with it.

We know it's a portal and not just an energy beam, because there's no hole in the top of the plane when the beam fades. Why spend money on a C.G.I. energy beam shooting up into the sky instead of just having Red Skull explode? In the first scene of "The Avengers," the Tesseract is described as a doorway, and at the end, it even teleports Thor and Loki back to Asgard. Some theorists even go so far as to suggest Red Skull is lending out the resources of HYDRA to Thanos so they can take over Earth together.

11 PEPPER POTTS IS DEAD

Gwyneth-Paltrow-Pepper-Potts-Falls

Where has Pepper Potts been since "Iron Man 3?" It's been four years and eight films since her last appearance in the MCU with her absence always being explained away by Tony as "she's busy." We're led to believe that they've broken up and Tony is just too embarrassed to admit it to his friends, but since when is Tony Stark embarrassed about anything? At the end of Tony's opening speech in "Captain America: Civil War," his teleprompter reads: "Now I would like to introduce the head of the foundation: Pepper Potts," and Tony's face looks like he's on the verge of tears.

His assistant says that she canceled, but that doesn't explain the look on Tony's face. The theory is that Pepper died as a result of the Extremis experiment and Tony has been keeping up appearances, even scheduling and canceling appointments to hide her death from the world. It would give a better explanation as to why he went back to being Iron Man after swearing off the suits at the end of "Iron Man 3" than that he was just addicted to the fight. He needed the distraction.

10 HEIMDALL HAS THE FINAL INFINITY STONE

Idris-Elba-Heimdall-Soul-Stone

The entirety of the MCU so far has been the story of the quest for the six Infinity Stones. We've seen five that we know of so far: Space (Tesseract), Mind (Loki's Scepter), Reality (Aether), Power (The Orb) and Time (Eye of Agamotto in the Nexus). The big question is: where is the Soul stone? This theory suggests that Heimdall has had it all along. In the "Guardians of the Galaxy" vision, the Soul Stone is shown to be orange, the same color as Heimdall's eyes and the gem on the front of his armor in "Thor: The Dark World." However, in Thor's vision in "Avengers: Age of Ultron," Heimdall's eyes are white.

In "Thor," Loki suggests that Heimdall has a power no one else has in Asgard, which is why he's in charge of watching over the nine realms. In "Thor: The Dark World," Heimdall tells Thor that he can see into nine realms and over 10 trillion souls. To top it all off, the location of the Infinity Stones seem to be foreshadowed with the acronym T.H.A.N.O.S.. Tesseract, Heimdall, Aether, Nexus, Orb, Scepter.

9 THE REALITY STONE WILL BE USED TO RECAST CHARACTERS

Avengers-MCU

One of the biggest questions of the Marvel Cinematic Universe since the beginning has been, "How will it continue?" Superheroes can continue to fight indefinitely when they're in print, but live action presents much more of a challenge. Not only will the actors continue to age until they're no longer suited for the roles, but typically actors want to focus on other projects as their careers continue. As much as we might be willing to watch Robert Downey Jr. suit up and fight evil well into his 60's, as an actor, he will eventually want to leave the role.

While there are plenty of heroes in the Marvel universe, a U.S. Agent movie just isn't going to have the same impact as a Captain America movie. The solution may already be present. In the comics, the reality gem has the power to grant its user control over reality. One who possesses the stone can create entirely different realities. One theory suggests that the reality gem will be used at the end of "Avengers 4" as a soft reboot of the universe, recasting long-time actors in the same iconic roles to prolong the life of the MCU.

8 THE CHITAURI INVASION WAS JUST A DISTRACTION

chitauri-secret-invasion-new-york-avengers

When you really think about it, the Chitauri Invasion in New York looked like it was destined to fail from the beginning. Loki set up the portal in the middle of one of the most densely populated cities in the world, where they would immediately meet resistance, instead of somewhere they could all come through the portal and attack with their full force. Even if the Avengers weren't there to fight them back, we know that S.H.I.E.L.D. was going to send in a giant missile to nuke New York anyway, so what exactly was their strategy?

What if it was a distraction for the Secret Invasion? The Secret Invasion storyline from the comics is perpetrated by the shapeshifting Skrull race, who invade the Earth and take the place of prominent heroes and political figures, but the Skrulls are owned in part by Fox, so it makes using them in the MCU tricky. However, in the Ultimate Comics, the Chitauri have the ability to shapeshift as well. Maybe while everyone was focusing on New York, another Chitauri invasion was happening right under everyone's noses, building Thanos' army on Earth before he even gets there.

7 PEGGY CARTER IS TONY STARK'S REAL MOTHER

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It was probably clear to everyone watching "Captain America: The First Avenger" that Peggy Carter and Howard Stark had some kind of intimate relationship before Steve Rogers showed up. Their friendship throughout "Agent Carter" shows that Howard trusts Peggy more than anyone else, and in the opening scene of "Ant-Man," we find that they still work closely with each other well into Howard's marriage. Howard was established as a bit of a womanizer from the very beginning, and in "Captain America: Civil War," Steve Rogers even says, "I can't believe Howard got married."

Sure, people grow and Howard might have met the right woman and wanted to settle down eventually, but the theory doesn't rely on Howard's infidelity. Another suggestion is that Maria wasn't able to carry children, so Howard went to his oldest and most trusted friend to act as a surrogate and carry their child. This would explain why Tony looks nothing like his fair-haired mother and another reason for his deep-seated daddy issues.

6 GROOT IS A GOD-LIKE IMMORTAL

Groot

Back in the opening scene of "Captain America: The First Avenger," as the Red Skull is trying to find the Tesseract, he looks at a carving of a tree on the wall and says, "Yggdrasil, the world tree. Guardian of wisdom and fate also." It seems like kind of a random line to throw in for no reason, but even before that, Thor describes Yggdrasil in "Thor" as the world's tree that connects the nine realms. Then in "Thor: The Dark World," Heimdall has an imprint of Yggdrasil on his chest plate.

In "Guardians of the Galaxy," it was established that any small piece of Groot, when preserved, will eventually regenerate into a living Groot, which suggests that he can basically go on living forever. The theory suggests that Groot came from a piece of Yggdrasil planted in the Earthly realm to be a "guardian." This would explain why no one in "Guardians of the Galaxy" seems to have ever seen anything like Groot before, and why his stat readout at the Nova Corps says, "Origin: X."

5  CAPTAIN AMERICA WILL DIE IN AVENGERS: INFINITY WAR

Chis-Evans-Captain-America-Dies

One of the big criticisms of the MCU so far has been an unwillingness to kill off any big players for reals. Pepper Potts fake died. Nick Fury fake died. Loki fake died twice. They might just be saving the big hero death for the big finale of the first three phases in "Avengers: Infinity War." Our first clue is in Tony's vision in "Avengers: Age of Ultron." He sees all the Avengers dead, but he specifically focuses on Cap, whose shield lies broken beside him.

Later in the movie, Scarlet Witch gives Steve a vision of himself finally getting that dance with Peggy who says, "The war's over, Steve. We can go home." Could this be Steve finally at peace? On top of all this, Chris Evans only has one movie left in his contract with Marvel and there's been no discussion of renegotiating, unlike Robert Downey Jr. who just signed on for more. Kevin Feige has stated that they can't reveal the title of "Avengers 4," because it will give away the ending of "Infinity War." Could that suggest that the title might be "Avengers: Fallen Son," the storyline that killed Cap in the comics?

4 THE INFINITY STONES WILL BE USED TO BRING VILLAINS BACK TO LIFE

Infinity-Gauntlet

Another major criticism of the MCU is that their villains are undeveloped and usually killed off too quickly to have an impact, like Red Skull, Iron Monger, Malekith, etc. Crossbones and Baron Von Strucker, two of the Avengers most deadly foes, barely got one scene each before they were unceremoniously killed off. One theory as to why Marvel keeps cutting down their heavy hitters with so many future films presumably on the horizon is that, just like the comics, they're not destined to stay dead.

In fact, they'll all be back to wreak havoc on the Avengers in "Avengers: Infinity War" through the use of the Infinity Gauntlet. The Soul stone has the ability to resurrect people from the dead and the reality stone has the ability to warp reality in any way the user sees fit. How great would it be to have the Avengers and Guardians already outmatched when Thanos raises all their worst nightmares from the dead. The Infinity Gauntlet has been the core of the MCU framework since "Captain America: The First Avenger" at least. Thanos is going to warp reality somehow, and this might just be the most terrifying way to do it.

3 NICK FURY IS SECRETLY A CLAIRVOYANT

Nick Fury poster for Captain America: The Winter Soldier

Nick Fury seems to always have plans within plans, and backup plans for his backup plans. Is he just the world's greatest tactical strategist, or is he hiding a superpower of his own? One theory suggests that Nick Fury has the gift of precognition. Let's look at the facts. He puts together a team of superheroes right before aliens invade New York. He has secret underground bunkers in case of attacks. He has a program to bring people back from the dead, conveniently before his favorite agent is killed. He even has secret helicarriers built. That's a lot of government funds that are going to seemingly ludicrous things.

It's not just insanely good preparation though. In "Avengers: Age of Ultron," Fury shows up at Hawkeye's farmhouse mere hours after the Avengers, when only Barton knew where he was flying. He also seems to know everything about the situation with Ultron despite the fact that he hasn't been with S.H.I.E.L.D. for quite a while at this point. Speaking of faking his own death, he had that highly unlikely scenario prepared pretty much right on the spot when he needed to go into hiding in "Captain America: The Winter Soldier."

2 THE HAND IS CREATING VAMPIRES

Hand-Vampires

In Season 1 of "Daredevil," Stick is sent to eliminate the Black Sky, the bringer of shadows, "the kind of weapon you don't want in your world," but when they get there, it's just a child. How can a child be such a dangerous weapon? In season 2, the Hand tells Elektra that she's the Black Sky, but despite being this incredible weapon, she's killed pretty easily in the next episode, suggesting the Black Sky is more than just a human who wants to kill. It's meant to be the progenitor of an army of vampires.

In both "Daredevil" and "Iron Fist," the Hand is draining people of blood, which as far as we can tell, is used to resurrect people from the dead in a ceremonial sarcophagus. Another telling factor is that Stick specifically decides to train Matt because he is blind. Who would have an advantage against creatures that hunt in the night? People who don't rely on the light. To top it all off, "Black Sky" is an obvious allusion to nighttime, when vampires hunt, and the Hand is trained to hide their heartbeats, which makes sense if they're dealing with creatures who thirst for blood.

1 STAN LEE IS UATU THE WATCHER

stan lee cameo MCU films

One of the longest-running theories in the MCU is about everyone's favorite cameo actor and creator of most of the heroes, Stan Lee. He's appeared in every MCU property to date, and nearly every live-action Marvel production since "The Trial of the Incredible Hulk" in 1989, whether owned by Marvel Studios or not. Even casual fans who don't know that Marvel and DC are different universes have noticed the same guy popping up in so many superhero films over the years, so is there an in-universe reason for the same face popping up around every superhero in multiple universes?

One theory suggests that Stan Lee plays a single character in each of these appearances, Uatu the Watcher. In the comics, the Watcher is an extraterrestrial being assigned to observe Earth and its solar system. Uatu also has the ability to peer into other alternate realities, exploring "What If?" continuities. This would explain why Lee has shown up in Marvel films owned by different studios always as a bystander around superhero happenings. Even if it turns out not to be true, it's a fun headcanon for Marvel fans to cling to. So fun, in fact, that Kevin Feige recently admitted that Stan Lee's cameos in "Guardians Of The Galaxy" and its sequel are a nod to it. 

Be sure to tell us in the comments what your favorite MCU fan theory is!