2) Andrea
Most of these changes made to characters on the show are just cosmetic, changing an aspect of their deaths or backstories. The TV series completely altered Andrea to her core, however. She might as well be a different character altogether.
On screen, Andrea is one of the show’s least liked characters. After siding with Shane over Rick and then entering into a relationship with the Governor, she was practically a minor antagonist. She did find some redemption in the end though, as she realized the error of her ways before eventually getting munched on by a zombie and shooting herself in the head.
In the comics, though, Andrea is another long-serving character. Far from being at odds with the group, she ends up being the long-term partner of Rick – to the extent that Carl calls her “mom.” She also becomes the group’s sharpest shooter. In the show, both of these characteristics are taken up by Michonne and original character Sasha, respectively.