Though the comic-book movie genre is the most prolific around right now, it’s interesting to note how much of that success has been found by wildly deviating from the source material.
2014’s X-Men: Days Of Future Past saw Wolverine being sent back in time, but in the comic the movie was based on, it was Kitty Pryde; in Avengers: Age Of Ultron, it was Tony Stark who created the titular villain, despite that mistake lying with Hank Pym in the comics; and in Batman v Superman, Batman murders goons without mercy, a big difference from the character’s strict moral code found on the page.
It simply wouldn’t be possible for most comic-books to be cleanly lifted and placed on the movie screen. Storylines have to be condensed or fleshed out, characters have to be axed if the studio doesn’t own the rights, and since comics are commonly more cartoonish and bright, most have to change in a big way.
And it’s usually the characters themselves who go through the biggest changes. You’ll be surprised by how massive certain alterations were, but whether or not they were warranted is firmly up for debate.