Marvel Studios and its Marvel Cinematic Universe have generally drawn rave reviews from longtime readers of Marvel Comics for being willing to faithfully adapt the treasured and storied source material - but adapting does not entail making an exact copy. As a result, there are plenty of MCU characters with completely different backstories than their comic book counterparts, though there’s almost always at least some level of homage at play.
When it comes to comparing Marvel backstories in the comics versus the movie, it’s a fool's errand, as the differences are more often than not a result of the change in medium more than anything. It’s best to think of the annals of Marvel Comics and the continuity of the Marvel Cinematic Universe as separate and distinct entities - not competing with one another, but complementary.
Everyone in the Marvel Cinematic Universe has heard Thanos’s personal backstory a time or two - it’s a tale he clearly loves telling. In essence, he thought that his homeworld of Titan was about to face a population crisis and suggested random mass slayings, “they called me a mad man,” and then the crisis happened, and he set about finding a way to eliminate half of all life in the universe. As one does.
The Marvel Comics version of Thanos, however, never had much of a choice, because he was approached by - and became infatuated with - the literal embodiment of Death at a very young age. Always appearing to the future Mad Titan as an attractive girl or woman, Death would remain a big part of his life from there on out, and pleasing her would provide most of the motivation for the actions that would make him the universe’s greatest villain. And once he got his first taste of ending a life, Thanos found he couldn’t stop.707Massive change?
All that is known of the MCU Nick Fury’s younger years is his military record, which includes time as a colonel in the Army and as a CIA operative before rising through the ranks of SHIELD to the position of director. Other than that, Fury is a bit of a blank slate - but it’s safe to say his personal history is a far cry from that of his comic book counterpart.
The Marvel Comics Fury also served in the Army as head of the Howling Commandos - but he did it back in WWII, mixing it up with both Captain America and Wolverine. Following the conflict, Fury was a trial subject for the Infinity Formula, which greatly extended his natural lifespan - and that allowed him to kick off an intelligence career spanning more than half a century.
Of course, these days, the original comic book Fury has been retired - to the moon, no less - and replaced with his son, Nick Fury Jr., who conveniently looks a whole lot more like Samuel L. Jackson.7411Massive change?
Very little time is spent on Mantis’s origin in the Marvel Cinematic Universe, but it’s a pretty simple one - she was discovered in a larval state on some alien planet by Ego the Living Planet, who might just be her father, and adopted because of her unique ability to put Ego to sleep. And that’s it, really, until she meets and joins the Guardians of the Galaxy.
The backstory of the comic book Mantis, who was associated with the Avengers long before she was a Guardian, is quite different and significantly more complicated than that of her MCU counterpart. This Mantis was born in Vietnam as an ordinary human, but quickly identified by a sect of Kree fanatics as the “Celestial Madonna.” Those alien cultists endowed Mantis with her telepathic and empathic abilities and trained her in combat until she was 18, and then mindwiped and dumped her in the streets of Saigon to find her own way to her supposed destiny of restoring the Cotati race - which is exactly what she ends up doing.605Massive change?
As seen in Captain Marvel, the Carol Danvers of the Marvel Cinematic Universe was once an ordinary human Air Force pilot until a chance encounter with the original, alien Captain Marvel. After a Kree device explodes in her face, Carol is endowed with a whole host of energy-based powers, setting off on a dual career as a space warrior/superhero.
For a long time, that was pretty much the story when it came to the comic book Carol, too - though she goes through a whole host of other monikers, including Ms. Marvel, Warbird, and Binary, before taking on the mantle of Captain Marvel - with the notable exception of the whole “ordinary human” part. A fairly recent plot twist in the pages of Marvel Comics reveals that, while Carol’s father was indeed an earthling, her mother, Marie Danvers, was actually the Kree champion Mari-Ell on a mission to assimilate with the Terrans - making Captain Marvel a half-Kree and heir to a role of prominence in the mighty Kree empire.587Massive change?