One of the more famous aspects of comic books, whether DC or Marvel, is the crossover event. Every so often, a villain will come about whom the entire rest of the fictional universe has to defeat, prompting a multi-month (or sometimes even multi-year) story arc across multiple separate books; from DC's Crisis on Infinite Earths back in the 1980s to Marvel's 2015 Secret Wars (the apparent source material of the current MCU saga), the crossover event has proved a reliable source of thrilling comic book stories for decades.
While the MCU hasn't adapted every Marvel crossover event, or even necessarily a large fraction of them, a decent proportion of its films and TV shows have adapted famous events. Oftentimes, the adaptations aren't a direct one-to-one replica of the crossover events; sometimes, it's as simple as a title or a core premise being the only element carried over. However, it's worth exploring the source material for all of these beloved films and shows, and comparing and contrasting the two.
8 The Ultimates (2002-04) - The Avengers (2012)
This limited series by Mark Millar and Bryan Hitch, one of the main series that kicked off the former Ultimate Universe (the comic birthplace of Spider-Man: Into the Spider-Verse's Miles Morales), follows a Nick Fury who closely resembles Samuel L. Jackson as he attempts to put together a ragtag team of government-sponsored superheroes under the banner of SHIELD. Eventually, the Ultimates (not the Avengers, in this comic) are tasked with facing off against the Chitauri, an invading alien species threatening to destroy humanity.
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While The Ultimates isn't a traditional crossover event, being the first appearance of all the Ultimate forms of its characters, it is a limited series effectively patterned like one; Millar and Hitch essentially skipped the traditionally-requisite solo series and simply went directly for the event book. It only fits, then, that it was used for the first MCU crossover movie. While the tone of the movie is much lighter (the Hulk never eats anybody, for instance), Hank Pym's role is largely folded into Tony Stark, and Loki is added as an explanation for the Chitauri incursion, among other minor details, The Ultimates and The Avengers stand as the closest one-to-one comparison between an MCU film and its source.
7 Age of Ultron (2013) - Avengers: Age of Ultron (2015)
This crossover event by Brian Michael Bendis and Bryan Hitch, patterned after the famous Age of Apocalypse event in the X-Men comics, features a dark alternate future in which Ultron has successfully taken over the world, and a ragtag group of the surviving heroes must try to defeat him.
Standing in contrast to the previous Avengers film, Avengers: Age of Ultron has little in common with its source comic beyond its title. The comic posits a universe in which Ultron has already won, right out of the gate, whereas the film is about the Avengers stopping a newly-made Ultron. However, there are a few similar plot beats between the two, with Ultron creating Sentinels to attack the Avengers (not called as such in the film due to the X-Men rights situation, but still clearly recognizable) and driving the Avengers into hiding.
6 Civil War (2006) - Captain America: Civil War (2016)
In this crossover event by Mark Millar and Steve McNiven, after a minor villain (Nitro) kills six hundred people in Stamford, Connecticut, the United States government passes a "Superhuman Registration Act" in an attempt to regulate superpowered individuals. This divides the Marvel Universe's heroes and villains, with battle lines quickly being drawn between the pro-registration side (led by Iron Man) and the anti-registration side (led by Captain America).
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Civil War strikes a middle ground in terms of how intact the story was from book to screen. Captain America: Civil War keeps the basic premise intact, along with the rivalry at its core, but it makes the story more personal, tying everything directly to the Avengers and centering the rivalry around Bucky Barnes. In this case, changes were likely unavoidable; Civil War, in its comic form, is a rather sprawling story heavily involving characters Marvel did not yet have access to. However, despite these changes, the film still manages to keep the spirit of the crossover intact, and stands as one of the most impressive MCU films.
5 Planet Hulk (2006) - Thor: Ragnarök (2017)
Written by Greg Pak, this 2006 crossover storyline ran through New Avengers and The Incredible Hulk, featuring the Hulk as a spacebound barbarian hero on the planet Sakaar.
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While one of the less direct adaptations, Thor: Ragnarök adapts the broad strokes of Planet Hulk as part of its storyline, with Hulk and Thor participating in gladiator games on the planet Sakaar. Numerous changes were made in order to fit the storyline into Thor's story, such as the Red King being replaced with Jeff Goldblum's Grandmaster, and Hulk being a willing participant in the arena. However, for fans of this famous story, it was a treat seeing the barbarian Hulk on the big screen.
4 The Infinity Gauntlet (1991) - Avengers: Infinity War (2018), Avengers: Endgame (2019)
In this massive crossover event, the Marvel heroes must come together to stop Thanos, who has used the Infinity Gauntlet to erase half of all life on Earth.
The Infinity Gauntlet is one of the most popular Marvel crossovers, to the point where many crossovers since have essentially repeated it (most notably Jonathan Hickman's Infinity from 2013, the source of the Black Order). Jim Starlin quickly made Thanos one of the most popular and enduring Marvel villains with this storyline, and it was almost inevitable that it would be an early pull for the MCU. While many beats are changed around, the films that finish off the Infinity Saga are a relatively faithful adaptation, keeping the core plot intact.
3 Marvel Zombies (2005-06) - What If...? (2021)
Written by Robert Kirkman of The Walking Dead and Invincible fame, this fan favorite non-canon limited-series crossover posited a world in which the Marvel heroes were overrun by a zombie virus.
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When Marvel announced a What If...? series for Disney+, it was inevitable that Marvel Zombies would find its way into the mix. While by no means a complete or direct adaptation, the What If...? episode is successful at carrying over the core premise in a more MCU-friendly manner. Marvel Zombies is one of the darkest things to be associated with the Marvel universe in recent memory, and it's impressive that a work under the watchful eye of the Mouse was able to carry that over at all.
2 Spider-Verse (2014-15) - Spider-Man: No Way Home (2021)
In this storyline stretching across all the Spider-Man books running at the time, an interdimensional villain named Morlun attempts to kill all of the multiverse's Spider-Men, causing the survivors to band together across universes in order to stop him.
Spider-Man: No Way Home, much like Into the Spider-Verse, adapts the core concept of this arc (interdimensional Spider-Men coming together to defeat a particular villain) while eschewing its specific beats. Rather than using nearly every version of Spider-Man ever put to print and inventing several of its own, NWH limits itself to only the cinematic Spider-Men. The film also replaces Morlun with Willem Dafoe's Green Goblin in the villain role.
1 Avengers: Disassembled (2004-05) - WandaVision (2021), Dr. Strange in the Multiverse of Madness (2022)
In this crossover storyline that started Bendis' Avengers run, Wanda Maximoff becomes dangerously unstable in response to the loss of her children with The Vision, rendering her reality-warping powers a major threat to the universe.
Both WandaVision and Dr. Strange in the Multiverse of Madness adapt parts of this storyline. WandaVision shows the leadup to Wanda becoming a villain, establishes her relationship with Vision more clearly, and establishes their children. Meanwhile, Multiverse of Madness finishes out the storyline, with Wanda becoming a multiversal threat using the Darkhold. Neither film adapts the storyline directly, with both making changes to fit the MCU, but the core beats are kept largely intact.
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