The Marvel Cinematic Universe loosely adapts plenty of comic storylines, but there are some that the mega-franchise could have done more with.

The Marvel Cinematic Universe is, without doubt, the most successful superhero film franchise ever created, with other thirty installments to its ever-expanding story, billions of dollars made at the box office over the span of fourteen years, and a massive following that exceeds even the popularity of its comic source material.

While the MCU seems to have perfected the art of comic book adaptation, it tends to do so loosely, putting its own spin on well-known storylines. As such, there are several massive stories in comics that the MCU has touched on, but could have expanded upon.

The Illuminati is a massively important organization in Marvel Comics, most commonly consisting of the superheroes Iron Man, Mister Fantastic, Professor X, Namor the Submariner, Black Bolt, and Doctor Strange. These individuals make decisions on a global scale, playing a major role in other crossover events like Civil War, World War Hulk, and Secret Invasion.

Doctor Strange in the Multiverse of Madness recently introduced the Illuminati to the MCU, albeit on Earth-838. While the concept was certainly in line with the comics, the members were quickly dispatched by the Scarlet Witch before they could properly live up to their comic book counterparts. Nevertheless, fans may still see a comics-accurate version of the Illuminati on Earth-616 in the near future.

The "Demon in a Bottle" arc is perhaps one of the most character-defining storylines in Tony Stark's comics history. Found in issues #120-128 in Invincible Iron Man, the story follows Stark as he attempts to stave off the villainous threat of Justin Hammer, all while battling his inner demons in the form of his alcoholism.

This storyline was touched upon in Iron Man 2, with Tony Stark facing off against Justin Hammer while also battling his own inner demons. The film, however, was juggling multiple storylines at once, with the more nuanced elements of "Demon in a Battle" getting lost in the shuffle.

Greg Pak's landmark "Planet Hulk," found in issues #92-105 of Incredible Hulk in 2006 and 2007, featured the titular green behemoth shot into space by the Illuminati, ending up on the planet Sakaar. Hulk is eventually hailed as the Sakaarson and crowned king after leading the people out of subjugation under the villainous Red Emperor.

Thor: Ragnarok included certain elements of "Planet Hulk" by featuring the green giant on the planet Sakaar as a gladiator alongside Thor. Several important characters from the comic storyline are also included, such as Korg and Miek. However, the film was ultimately concerned with Thor's story rather than Hulk's and does not adequately feature Pak's iconic storyline. Hulk fans should not fear, however, as rumors have recently been swirling that the MCU could still adapt the "World War Hulk" event that followed "Planet Hulk" in the comics.

The Kree-Skrull War is a vitally important conflict in the Marvel Universe, found in Avengers #89-97. The story depicts the ongoing conflict between the Kree and Skrull empires, which spanned across galaxies and brought destruction upon countless innocents. This conflict would become the basis for many future storylines, including the Secret Invasion.

The war between the Kree and the Skrulls is a primary part of Captain Marvel, where the conflict is originally depicted as a black-and-white issue, only for Carol Danvers to later discover that the issue is far more nuanced than she thought. While the film manages to capture some of the symbolic themes of the comic event, it shows very little of the war itself, leaving far too much to the imagination.

Based on the mythological event depicting the deaths of the gods of Asgard, "Ragnarok" occurs in the Marvel Universe in 2004 (Thor volume 2, #80-85). In this story, Loki brings about the destruction of Asgard and all its inhabitants, with even Thor dying in the process. This event, however, is cyclical in nature, as Ragnarok occurs multiple times throughout the eons, with the gods eventually regenerating.

As the title suggests, Thor: Ragnarok relies heavily on this comic storyline, featuring the destruction of Asgard at the hands of Surtur the fire giant. While the general outcome of the film is the same as in the comics, the build-up is entirely different, with Taika Waititi's universally beloved film only loosely adapting the events of the source material.

"Extremis" is a storyline found in the first six issues of Iron Man volume 4 in late 2005 to early 2006, immediately preceding the Civil War. This story features a massive upgrade for Tony Stark, as he not only increases the power of his suit but also inherits certain biological abilities that give him greater command over his technology.

Iron Man 3 features several major elements of the "Extremis" storyline from the comics, even overtly using the term throughout the film. However, the film ends without Tony Stark's major enhancements from the comics, making the movie adaptation of the storyline far less impactful on the character.

While not a direct storyline, Matt Fraction and David Aja's run on Hawkeye is largely considered to be some of the best work featuring Marvel's signature archer. Featuring Clint Barton and Kate Bishop working out of Clint's newly-owned apartment building in New York, the series re-contextualizes both characters and their mentor-pupil relationship.

The Disney+ series Hawkeye was heavily inspired by this run, with the overall tone and premise closely resembling Fraction and Aja's work. However, the series could have expanded more on its adaptation, further exploring the relationship between Clint and Kate, which it could still yet do in a rumored second season.

The Civil War event is one of the most important crossovers in Marvel Comics history, as the superheroes of the world are divided regarding the notion of registering with the government. Pitting Captain America against Iron Man, an all-out war begins, with both sides suffering major losses along the way.

Captain America: Civil War is one of the best entries into the franchise and a game-changer for the Avengers, even introducing several major characters to the MCU. However, it lacks the worldwide impact of the comic book event with which it shares a name and is ultimately a series of skirmishes rather than an all-out war.

The "House of M" storyline features the mental descent of Wanda Maximoff, who, after discovering her children were actually conjured by Mephisto, recreates reality as she sees fit, giving the Avengers and X-Men each their greatest desires in life. After this reality falls apart, however, Wanda reverses her hex to restore the normal world with one exception: no more mutants.

Many fans believed that the "No More Mutants" finale of "House of M" could be reversed for the MCU following the events of WandaVision and leading up to Doctor Strange in the Multiverse of Madness. While the latter of these projects did depict the Scarlet Witch's descent into madness and subsequent villainy, it failed to establish anything about the mutants in the MCU, as many had hoped. Even so, the "House of M" storyline could still occur in full within the MCU if Wanda Maximoff indeed survived her sacrifice at the end of Multiverse of Madness.

"Age of Ultron" occurred in Marvel Comics in 2013 in the form of its own miniseries crossover event. In this storyline, an alternate universe is explored when Ultron has annihilated humanity and taken over the world, installing his own regime.

Many fans have criticized Avengers: Age of Ultron for severely toning down the "Age of Ultron" storyline from the comics. In the film, Ultron only attempts to take over the world, failing after the Battle of Sokovia, and audiences never get to see what a world dominated by metal would truly be. Marvel Studios did make up for this blunder much later, however, with the final few episodes of What If...? exploring a parallel reality wherein Ultron possesses the Infinity Stones and does indeed destroy humanity.

NEXT: 10 MCU Characters Unlikely To Transform Into Their Superpowered Comic Counterpart

Jordan Iacobucci is an avid reader and movie fan, and has been since childhood. Jordan is known among his friends as the Marvel and Star Wars nerd, and even wrote a thirty-page college dissertation about Spider-Man! He is currently obtaining an English degree and lives outside Raleigh, North Carolina with his family. His other interests include working with children, reading, and music.