Kick-Ass is pretty unusual when it comes to comic book adaptations. Most comic book movies are based on a character, and may take inspiration from a few specific stories. Some, like Watchmen and 300, are direct adaptations of a specific story. Kick-Ass falls under the second category. However, unlike other direct adaptations ,the rights to the film version of the comic were sold before the first issue was published. Mark Millar pitched the idea to Matthew Vaughn and Matthew Vaughn liked it so he and Jane Goldman wrote the movie while Mark Millar wrote the comic. They all worked very closely together when putting the story together.
Because the circumstances behind bringing Kick-Ass to film are so unique, it's interesting to take a look at some of what they changed and kept when making the transition.
Kick-Ass: Kick-Ass is pretty much exactly like he was in the comic book. There are only two differences that I can think of. First, Aaron Johnson is a brunette while Dave was blonde in the original. Second, the Kick-Ass costume has a hole cut for the mouth in the movie while the mouth remains covered in the comic. Obviously these changes are quite minor. The costume is very faithful to the original costume, personally I think it might have looked a little bit cooler if they covered the mouth. Think of Peter's wrestler costume in the first Spider-man movie. However, it's probably a lot easier to breathe without the mouth covered. Also, they didn't really want to make him look cool, so it works. Aaron Johnson was pretty much the perfect Dave and exactly how imagined him. That might be because I saw the trailer before I read the comic, but I still definitely think he fully embodied the character the way he was written.
Hit-Girl: Hit-Girl's costume is slightly different from her comic book counterpart, but character wise she pretty much exactly the same. Chloe Moretz did a great job as Hit-Girl. She was very entertaining with her great stunt work and the delivery of her profanity-filled lines. Some people find it offensive to have such a young actress playing a character who uses this kind of language and kills people, but I thought it was hilarious. When watching Kick-Ass, you should remember that it's not for young viewers and that you should take it too seriously.
Red Mist: Red Mist was portrayed a little bit differently in the movie than he was in the comic. This is partially due to some of the changes in the structure of the plot. I'll get into some of the plot details in a later section, but there are a few things I can cover here. SPOILERS The comic book Red Mist really didn't seem like he was supposed to be nerdy. When he meets Kick-Ass, Kick-Ass sees him as kind of a cool guy. It's made clear during the story that he's not very brave. When he betrays Kick-Ass, you get the sense that he has been a bad guy the whole time and was completely pretending when he befriends Kick-Ass. If I were casting Red Mist based on the impression I got of the character from reading the comic, I might have casted someone like Josh Zuckerman who starred as Ian in the 2008 movie Sex Drive. However, just because this version of the character was different than I imagined doesn't mean I thought it was worse. Christopher Mintz-Plasse was great as Red Mist. Since his hilarious role as McLovin in the hit comedy Superbad, Mintz-Plasse has kind of been type casted as sort of nerdy loser characters. That was probably already what the movie makers had in mind for the character even before they casted him, so assuming that's what they were going for he was perfect. He was funny as usual as Red Mist. This movie version of Red Mist was slightly wimpier and nerdier than the comic book version. However, he's more of a sympathetic character because you can see at one point that he's not completely bad. The movie version of the costume is cooler than the comic version. It includes a lot more black, but keeps the original Red Mist "M" emblem on his chest. It's also worth noting that for some reason his last name went from Genovese to D'Amico.
Big Daddy: Big Daddy is definitely the most altered of the main characters. For one thing, his story is very different (I'll get to plot detail later). Also, his whole persona has changed. His costume is the most different, going from something rather plain (full mask, visible hair, jacket) to a costume that is an obvious homage to Batman. Personality wise, there are two sides to Big Daddy. SPOILERS On the one hand he's a very dark character who is driven to take down D'Amico and is an expert at killing. On the other hand, his persona as Big Daddy uses a voice that imitates Adam West's campy Batman from the sixties. The feel I got from the comic book Big Daddy was that he was attempting to be something closer to the Punisher. To sum it up, movie Big Daddy looks like modern movie Batman, talks like the 60's Batman, and acts like the Punisher.
(comparison images courtesy of IGN.com http://movies.ign.com/articles/108/1082206p1.html )
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