It's easy to see just how many mediums of entertainment the MCU has affected in the years since Iron Man first blew his way onto screens back in 2008. But, besides the box-office, no other entertainment medium has been as effected by the MCU's ascendancy than the world of Marvel's comics.
The Legacy of the "Daywalker"
Although Marvel had some fleeting and not very well received moments during their four earlier forays into cinema, it wasn't until 1998's Blade that people, production companies and filmmakers were like "oh, so that's how you make a comic movie!"
Before Wesley Snipes owned the role of the superhuman, half vampire hunter/badass, comic book Blade was a fairly different character. He had the long life, the ability to sniff out vampires and other supernatural beasties, and was immune to vampire bites.
But when the inaugural movie adaptation rolled around, Blade became the "Daywalker," an infamous half human, half vampire hunter extraordinaire who was blessed with all of the strengths of a vampire, but zero of their weaknesses. Thanks in some part to Whistler's serum.
Due to the success of Blade's cinematic reworking, the comic book iteration saw some sneaky changes start to happen. In an arc in 1999's Peter Parker, Spider-Man, Blade inherited his cinematic vampiric abilities after being bitten by Morbius, the title of "Daywalker," and a costume that was closer to the swag of the movies.
Speaking of costume alterations...
After Bryan Singer brought his vision of the X-Men to the screen, in 2001's The New X-Men #114, the mutant heroes saw their super iconic yellow and blue spandex go flying out of the window and replaced with shiny new black leather outfits. Which you could probably hear coming from a mile off. So much for stealth operations when you've got Beast creaking about on the ceiling.
But, trust (Lord) Joss Whedon to come in and shake things up a tad. In his and John Cassaday’s Astonishing X-Men, the heroes fought their way out of the tight leather, and right back into their even tighter spandex costumes. Hooray for elastane!
Even Clint managed to bag himself a new look after 2012's The Avengers! In Matt Fraction and David Aja’s Hawkeye - also released in 2012 - the well observant hero got the chance to slip off his purple mask and suit, in exchange for a more casual badass sunglasses wearing hero look.
In a not particularly surprising move, Guardians of the Galaxy's Lord of the Stars had his comic getup completely ditched, aligning his look with the movie - the duster jacket, Halo-esque blasters and that badass mask/helm.
When Nick Fury was first drafted into the 'Ultimates' canon in 2001, his entire aesthetic was altered, right down to the fact that he was now African-American and, suspiciously, looked very similar to the badass that is Samuel L. Jackson.
Later Jackson was to discover the usage of his likeness, and got in contact with Marvel - not to reprimand them, but to state that any future movie appearances by Fury should be played by him. Check out the big brain on Jackson!
Peter Parker and his wrist mounted web shooters are synonymous with each other, as we all know by now. But when Sam Raimi's Spider-Man first released in 2002, the creative team decided to do away with them, and have Parker create biological webbing. Bold move.
It took 2 years before the comics followed suit, and in 2004's The Spectacular Spider-Man: Disassembled, Spidey was subjected to an incredible transformation that slowly started making him more spider than man, including the ability to create his own webbing.
The Maximoffs: Mutants or Experiments?
Scarlet Witch and Quicksilver, Marvel's stalwart sibling pair of mutants... aren't actually mutants any more, nor were they ever, according to their recent retconning. The move which perfectly aligns the two heroes with their AoU counterparts first occurred in Uncanny Avengers #4, where the two found out that they were failed experiments of the High Evolutionary.
Many a fan saw this move as an of F.U. to Fox, thinking it was intended to disparage Fox's vision of mutant Quicksilver. Which would be funny if it was, but, to be honest, Joss Whedon has spoken out on numerous occasions of his love for Scarlet Witch and Quicksilver, so I'm guessing the retcon occurred so he could throw them into the movie.
Which wasn't a bad idea at all. I mean, they are Marvel's IP after all. They're free to do what ever they want with them on the page and the screen.
Anyway, the list of amendments is almost never ending, but for the sake of ending this, I'll end it here.
Comics have to stay fresh and be enticing enough to introduce a new generation of people to their epic lores, and seeing as the MCU has a ludicrously wide reach, it's understandable why Marvel has made so many changes to bridge the gaps between their IPs.
Let's just hope they don't make too many more drastic changes...
(Sources: i09, WIki)