While each Marvel Studios film stands alone as a conversation-starting new release, every Marvel movie unveils a piece of the larger Marvel Cinematic Universe. The meticulous planning behind the MCU has inspired close study and fueled limitless speculation from legions of loyal Marvel fans. Now, Taika Waititi's new film, Thor: Ragnarok, set to add another piece to the MCU's puzzle. Since the Russo Brothers' Avengers: Infinity War is set to deliver on some of the MCU's longest-teased stories in 2018, rampant fan speculation about the future of the MCU is at an all-time high.

RELATED: What The Hela: 15 Things You Must Know About Thor: Ragnarok's Big Bad

Now, CBR is taking a look at some Thor fan theories that might actually be true. In this list, we'll be digging through some of the most popular fan theories about the MCU's Thor, the other Asgardians and the other Avengers featured in Thor: Ragnarok, namely Doctor Strange and the Hulk. To see how these theories check out, we'll also be looking at relevant comments from some of the creative minds behind the MCU and any other available evidence. While "Phase Three" of the MCU will barrel on until at least 2019, these theories might unlock the secrets that the future of the MCU holds in store for fans around the world.

SPOILER WARNING: This entire contains a comprehensive summary of speculation about the MCU that may spoil future storylines in films like Thor: Ragnarok and Avengers: Infinity War.

15 THOR HAS THE SOUL STONE

MCU Thor Mjolnir Chris Hemsworth

Since Kenneth Branagh's Thor teased the role of Infinity Stones in the MCU in 2011, Marvel's films have revolved around those all-powerful artifacts. As the MCU has built towards an adaption of Jim Starlin, Ron Lim and George Perez's The Infinity Gauntlet, the Space, Mind, Power, Reality and Time Stones have all appeared onscreen. The location of the last Stone, the Soul Stone, is one of the MCU's biggest remaining mysteries.

One fan theory posits that the Soul Stone is hidden inside of Thor's hammer, Mjolnir. According to this theory, Thor's hammer can only be wielded by the "worthy" because the Soul Stone tests a prospective wielder's soul. That could explain why Hela destroys the hammer in the trailers for Thor: Ragnarok. The fact that other Stones have already been hidden in objects like Loki's Scepter and Doctor Strange's Eye of Agamotto also lend credence to this theory.

14 HEIMDALL HAS THE SOUL STONE

Heimdall Idris Elba

Thanos is one of Marvel's most powerful cosmic threats, and Josh Brolin's version of the cosmic villain will gather the Infinity Stones in 2018's Avengers: Infinity War. According to one fan theory, Thanos' name also serves as an acronym that reveals the locations of the Infinity Stones. That has held true for the Tesseract, the Aether, Doctor Strange's Necklace, the Orb, and Loki's Scepter, and that means that "H" must hold the Soul Stone.

According to one popular fan theory, Heimdall, Idris Elba's all-seeing Asgardian watchman, has the Soul Stone. Given the Infinity Gauntlet's color scheme, the Soul Stone should be orange, just like the gem in Heimdall's armor. Heimdall also has orange eyes, which he can use to keep watch over "10 trillion souls." That would also explain why Heimdall's eyes were white in the apocalyptic possible future Thor glimpsed in Avengers: Age of Ultron, after Heimdall presumably lost the Stone.

13 HELA'S RELOCATION

Hela Destroys Mjolnir

In what's arguably the most memorable moment from the Thor: Ragnarok trailers, Cate Blanchett's Hela catches Mjolnir and shatters it in her bare hands. In Ragnarok's earlier trailers, this moment took place in an alleyway, but more recent trailers showed it taking place in an open field. According to director Taika Waititi, this scene originally took place right after Chris Hemsworth's Thor consulted with Doctor Strange, as seen in the post-credits sequence of 2016's Doctor Strange.

Initially, Thor appeared to confront Hela alone in the alleyway. In the revised version, Thor confronts Hela while standing next to Loki on the field. Waititi has revealed that this scene also includes Odin, and said that it relocated to give Odin and Thor's reunion a more peaceful backdrop. That's still left some fans wondering if Hela or Loki's role in the film changed or the film's over-arching structure was affected by the relocation.

12 MARVEL COULDN'T MAKE PLANET HULK

Hulk Thor Ragnarok

Even though Thor: Ragnarok is a Thor movie, Mark Ruffalo's Hulk will be a big part of the film. As seen in the film's trailers, the Hulk and Thor will battle in an alien gladiatorial arena in a nod to the 2006 story "Planet Hulk." Originally by Greg Pak, Carlo Pagulayan and Aaron Lopresti, "Planet Hulk" stands as the most well-received Hulk story in recent memory. That's left some wondering why "Planet Hulk" is part of a Thor movie instead of a Hulk movie.

Before the MCU really got going, Universal Pictures obtained the distribution rights to the Hulk's movies. While the Hulk can appear with ensembles like The Avengers, Ruffalo confirmed rumors that those rights issues have kept the Hulk from appearing on his own since 2008's The Incredible Hulk. Despite that, Marvel Studios President Kevin Feige said that the Hulk's upcoming cinematic appearances will form a thematic trilogy.

11 THERE ARE TWO INFINITY GAUNTLETS

Thanos Infinity Gauntlets

Before audiences knew how important the Infinity Stones would be to the MCU, some eagle-eyed viewers saw an Infinity Gauntlet sitting deep within Asgard's vaults in 2011's Thor. After Avengers: Age of Ultron ended with Thanos picking up another Infinity Gauntlet in 2015, some fans noticed that Thanos' gauntlet was left-handed, while the Asgardian gauntlet was right-handed.

Around then, Marvel Studios head Kevin Feige confirmed that there were two Infinity Gauntlets in the MCU. Since Feige commented on the distinction between the two gauntlets in public, it seems quite possible that the Asgardian gauntlet will eventually come back into play. That's fueled some speculation as to whether Thanos and the MCU's heroes might race each other to gather the Infinity Stones first. If that happens, fans have wondered if that means an Avenger, an Asgardian or a Guardian of the Galaxy could eventually use the Infinity Gauntlet against Thanos.

10 THOR DOESN'T NEED MJOLNIR

thor lightning powers

In Unworthy Thor and Marvel's other ongoing comics, Thor Odinson has spent the last few years without Mjolnir. Since Hela will seemingly destroy his hammer in Thor: Ragnarok, the MCU's God of Thunder could land in a similar place for the MCU's foreseeable future.

As revealed in Ragnarok's trailers, Thor appears to summon lightning without Mjolnir. While there's some comic book precedent for Thor manipulating energy without Mjolnir, some fans believe that Thor's arc in Ragnarok will mirror Tony Stark's arc in Iron Man 3. In Shane Black's 2013 film, Iron Man learned that the true power of his heroism came from within himself, and not from his high-tech armor. In 2017, Jon Watts' Spider-Man: Homecoming had Spider-Man make a similar realization. If Thor comes to a similar conclusion, that would complete the narrative arc that began in Thor, where found validation through Mjolnir's power.

9 TONY STARK HELPED HULK LEAVE EARTH

Close-up of Hulk with a serious expression piloting the quinjet

Mark Ruffalo's Hulk hasn't been seen onscreen since he flew into the sunset at the end of  Avengers: Age of Ultron. While that kept him from choosing sides during 2016's Captain America: Civil War, it's still unclear how he left Earth and traveled to the alien planet Sakaar.

According to one fan theory, the Hulk had a little help from Tony Stark. In the MCU, Robert Downey Jr.'s Iron Man and Bruce Banner formed a bond around their mutual love of science. Banner said that he left the Avengers to keep the Hulk from hurting anyone else, and Stark's Hulkbuster armor suggests that he recognized the potential threat the Hulk posed, too. According to this theory, Iron Man quietly helped Banner plan his escape. That could potentially drive a wedge between the MCU's heroes, and it hints at the overprotective mindset Iron Man had Civil War.

8 THE GRANDMASTER IS A CELESTIAL

Jeff Goldblum Grandmaster

While Hela will likely be Thor: Ragnarok's main villain, Jeff Goldblum's Grandmaster is also set to give Thor some trouble. In comics, the Grandmaster is one of the Elders of the Universe, who's been behind stories like Contest of Champions. Regardless of his role in Ragnarok, The Grandmaster may also be one of the most powerful beings in the MCU, a Celestial.

After the reality-altering aliens were introduced in 2014's Guardians of the Galaxy, audiences got their first real idea of the aliens' immense power with Kurt Russell's Ego in 2017's Guardians of the Galaxy Vol. 2. According to one theory, Goldblum's Grandmaster may be one of these ancient aliens. This theory came to prominence after a "Celestial" variant of the Grandmaster's Funko Mystery Minifigure popped up online. While that doesn't confirm the character's Celestial status, it suggests that the Celestials will play at least some role in the MCU's future.

7 ODIN HAS THE SOUL STONE

Odin Anthony Hopkins

If he's anything like his comic book counterpart, Anthony Hopkins' Odin should be one of the most powerful characters in the MCU. While Odin's Odinforce abilities usually come from within, his MCU powers could come from another source, the Soul Stone. According to one fan theory, Odin has hidden the stone in his empty eye socket and used its power to make Asgard an ageless paradise. That could also be why Odin's energy and Asgard both share an orange tint, which would match up with the Soul Stone's reported color.

In order to access its power, the Soul Stone requires sacrifice. According to the theory, Odin sacrifices part of himself during the "Odinsleep" to keep the Soul Stone charged. Since Tom Hiddleston's Loki cast Odin out of Asgard and took his place during 2013's Thor: The Dark World, Odin's Infinity Stone could be especially vulnerable without its watchful keeper.

6 LOKI IS STILL WORKING FOR THANOS

Thanos Loki Thor concept art

In both comic and film, Thor and his adopted brother Loki have one of Marvel's most tumultuous relationships. They can go from working together to battling each other to the death at a moment's notice. Although the two Asgardians haven't seen each other since Loki began impersonating Odin at the end of Thor: The Dark World, they'll meet again in Thor: Ragnarok.

As Ragnarok's trailers and Avengers: Infinity War's concept art have suggested, Thor and Loki appear to be working together on somewhat friendly terms. One fan theory suggests that they might not stay that way. In 2012's The Avengers, Loki agreed to capture the Tesseract for Thanos in exchange for Earth. While that initial effort failed, the theory claims that Loki could still give Thanos the Infinity Stones that are hidden in Asgard, possibly in exchange for the right to rule Asgard forever.

5 MAGIC'S INCREASING ROLE IN THE MCU

Doctor Strange Beneditch Cumberbatch

In Norse mythology, Ragnarok is the end of all things. While it probably won't be the end of the world in the MCU, it could still take some major power players like Odin off the field. If that happens, it would leave the MCU's heroes without many cosmic allies who could aid in their fight against Thanos.

According to one theory, the MCU's heroes could find new powerful allies from the world of Doctor Strange if Asgard falls. Scott Derrickson's 2016 film, Doctor Strange, was filled with powerful artifacts like the Staff of the Living Tribunal, the Eye of Agamotto and the Wand of Watoomb. In comics, these items are all linked to omnipotent cosmic beings who can reshape reality on a whim. The theory suggests that Doctor Strange and the MCU's heroes could turn to one of these beings if their impending struggle against Thanos takes a nasty turn.

4 WHY CAPTAIN AMERICA COULDN'T LIFT MJOLNIR

Captain America attempts to lift Mjolnir from a table

On occasion, Captain America has been one of the few comic book heroes who has been "worthy" enough to lift Thor's hammer. During 2015's Avengers: Age of Ultron, Chris Evans' Steve Rogers tried to lift Mjolnir, but was only able to move it a few millimeters. One fan theory suggests that the MCU's Cap couldn't lift Thor's hammer because of his former sidekick, Sebastian Stan's Winter Soldier.

As revealed in 2016's Captain America: Civil War, Rogers knew about the Winter Soldier's crimes, including the murder of Iron Man's parents, before he publicly acknowledged them. Captain America didn't share this information with Tony Stark, and that lie made him "unworthy" to wield the hammer, according to the theory. Since that information is now out in the open, the theory goes on to speculate about the possibility that Captain America might finally lift Mjolnir during Avengers: Infinity War or the fourth Avengers movie.

3 THOR WILL USE JARNBORN

Thor Jarnborn

Even thought Thor Odinson hasn't wielded his hammer since 2014, he hasn't been completely defenseless. Since he lost Mjolnir, Thor's been using Jarnborn, a Dwarfin axe he used in his youth. Created by Jason Aaron and Esad Ribic in 2010's Thor: God of Thunder #1, the so-called Wrecker of Worlds is supposedly sharp enough to cut through a Celestial and can be used as an indestructible shield. Other than Thor, the axe has also fallen into the hands of powerful villains like Baron Mordo, the Apocalypse Twins and Kang the Conquer.

If Thor leaves Thor:Ragnarok without his hammer, many fans believe he'll pick up Jarnborn before his next adventure in 2018's Avengers: Infinity War. Chris Hemsworth has dropped hints that comic fans will recognize Thor's next onscreen weapon. Some of the concept art for the upcoming Avengers movie shows Thor holding a weapon with a handle that looks similar to Jarnborn's handle.

2 HELA WILL BE LADY DEATH IN INFINITY WAR

hela cate blanchett helmet

In Marvel's classic 1991 storyline The Infinity Gauntlet, Thanos assembled the all-powerful Infinity Gauntlet to impress Mistress Death. Thanos even killed half of all life in the universe as part of his attempts to court Marvel's living embodiment of death. Since that plot might be too abstract for the MCU, some fans believe that Cate Blanchett's Hela may take Death's place in Avengers: Infinity War.

Early concept art suggests that Death was supposed to be introduced to the MCU in 2016's Doctor Strange, but her role was removed during one of the film's rewrites. In the trailers for Thor: Rangarok, Hela goes out of her way to describe herself as the Goddess of Death. Since those two characters were already so similar, this theory suggests that they were simply merged into Hela. Marvel has also hinted at this idea by teasing a budding romance between Thanos and Hela in the comics.

1 JANE FOSTER WILL BECOME THOR

Thor Jane Foster

In Thor and Thor: The Dark World, Natalie Portman played Jane Foster, Thor's longtime love interest and supporting character. Since then, Foster has been conspicuously absent from Thor's other appearances in the MCU. Although Portman has said that she thinks she's "done" with the Marvel movies, that's left some fans wondering if Jane might reappear and pick up Mjolnir to become a female Thor.

In comics, Jane Foster has been Marvel's Thor since 2014. While that storyline caused some controversy it's generally been one of Marvel's more successful reinventions in recent years. Even though Chris Hemsworth's days as the God of Thunder might be numbered, recasting Jane Foster, or another female character like Tessa Thompson's Valkyrie, as Thor would be a logical way to ensure the character's legacy. Since the MCU isn't showing signs of slowing down soon, a female Thor could help guide the Avengers into the next decade.

Keep it locked to CBR for all the latest on Thor, Thanos and the MCU. Let us know which theories you think are true in the comments!