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.
Hela, the Goddess of Death, shows up out of nowhere in Thor: Ragnarok to reveal herself as Thor and Loki’s much older (and much more powerful) sister, who had been banished by Odin all this time for her fatal obsessions. But that backstory is not at all accurate to the Hela of Norse mythology - or to the Hela of Marvel Comics.
In both the traditional telling of her story and her Marvel Comics canon, Hela rules over the realm of Hel and is not the adoptive sister of Loki - she’s his daughter. If that’s not strange enough, her giant pal the Fenris Wolf is also Loki’s child in this continuity, as is the World Serpent and Odin’s eight-legged horse. All of which, again, is mythologically correct.880Massive change?
Split between Guardians of the Galaxy Vol. 1 and 2, Peter Quill’s origin as Star-Lord centers around an alien abduction following the tragic demise of his mother, Meredith Quill - both of which have a lot to do with the cosmic origins of his father. Eventually, Peter learns that his dad is actually a being of unfathomable might known as Ego the Living Planet, but he also learns that Ego was responsible for his mother’s cancer, and so Peter has to eliminate him shortly thereafter.
In the comics, Star-Lord was also captured as a child following his mother’s demise, but neither event had anything to do with his father - though his dad does happen to be an important cosmic figure in this continuity, too. Known as J’son of Spartax, Peter’s comic book father is a bit of a totalitarian and usually as antagonistic toward the “backwater apes” of Earth, but he’s most often depicted as a few steps short of supervillainy. He also only wiped Meredith's memories of him instead of slaying her, so he and Peter are on significantly better terms.782Massive change?
Drax’s MCU origin is as tragic as it is simplistic. He was living a peaceful life on his home planet until Ronan the Accuser showed up and slayed his family and half of his people on Thanos’s orders. From there, Drax sets off on a life of bad decisions that lands him in an interstellar jail, where he becomes a founding member of the Guardians of the Galaxy - and eventually gets his revenge.
The themes of revenge are considerably more direct when it comes to the comic book canon of Drax. Believe it or not, Drax was once human saxophonist Arthur Douglas, who was enjoying a nice drive with his wife and daughter when Thanos showed up out of nowhere and offed them all for fun. Feeling bad about the whole thing and wanting to keep his son in check, Thanos’s father, A’Lars, uses his cosmic abilities to resurrect Drax as an incredibly powerful engine of vengeance and sets him on a lifelong quest to slay the Mad Titan.
Drax’s daughter also eventually returns as a bad, bikini-clad space psychic, but that’s a story for another time.754Massive change?
Before partnering up with Rocket, the personal history of the original Groot was largely unknown - and probably always will be, given that that character perishes in Guardians of the Galaxy, only to be replaced by their adorable progeny. Presumably, he’s just an alien tree from a planet of alien trees.
But the comic book Groot is a member of the Flora colossi race who once referred to himself as the “Monarch of Planet X” and fancied himself a cosmic warlord - though that eventually proved to be a bit of a front once he softened up and joined the Guardians. In his more villainous days, Groot was perfectly capable of speech, which he would mostly use to threaten and cajole his allies. Over time, however, he lost the ability to speak thanks to the congenital hardening of his vocal cords.672Massive change?