1) Carol
The other character who was pretty much 100% altered in the transition from the page to the screen is Carol. TV fans will know her as having one of the strongest, most transformative character arcs on the show, as the horrors of the apocalypse have made her grow from a timid, shy woman into a badass, strong-willed pragmatist. She’s been around for the length of the series thus far and it would be a big surprise if she was to be killed of. In the comics, however, basically none of these attributes apply.
First of all, comic book Carol is a much more skittish person, with latent psychological issues that were brought out by the trauma of the outbreak. Needing companionship to keep her sane, she starts to crack up once Tyreese cheats on her. After Lori and Rick turn down her offer of a three-way relationship (!), Carol commits suicide by letting a zombie bite her on the neck, seemingly feeling a sexual pleasure as she dies.
The journeys of the two Carols across the series are simply diametrically opposed to each other, making hers the best example of how liberally The Walking Dead TV show borrows from the comics.