I'm pretty sure by the end of the season we'll be introduced to "The Saviors" led by Negan. He's pretty much the worst villain in The Comic Book.

In the Comic Book he's the one responsible for bashing Glenn's in with a barbed wire baseball bat. Given how much they switch things around and change things up though, I've no idea if this'll happen. For instance in the Comic Book Tyreese is Rick's right hand guy and survives much longer than he did on the TV Show.

The Female leader of Alexandria was switched though...in the comic book it's a guy named Douglas, and they decided to gender switch that role.