Note that there are spoilers below for The Walking Dead comic books.
Earlier this week, The Walking Dead creator Robert Kirkman, who writes the comics and serves as both a writer and executive producer on the television adaptation for AMC, told Entertainment Weekly that the episode coming up in two weeks will feature the first TV appearance of a fan-favorite character from the comics.
“There’s a new character added,” said Kirkman of episode 8. “A big deal fan favorite from the comic book is introduced into the show in this episode, so be on the lookout for that.”
The magazine assumed that the character in question would be Tyreese--which is probably right, not only because the timing seems about right but also because he's got one of the most iconic scenes at the prison (look out for him to hit the gym shortly after he joins the cast if it is him) -- but that doesn't mean we can't think about what other characters might show up.
He and Abraham were the ones suggested by Entertainment Weekly, but of the people on this list, he's one of the less likely ones to appear soon...not that I don't expect to see him.
While Aaron is a popular character, and it can't hurt things to have more diversity in the series (he's gay and has a partner living with him at the settlement), he's part of the whole Alexandria Safe Zone/Hilltop Colony thing that's been going on for the last 20 issues or so. Expect that particular setting to take a while to find after the prison ends, since going from one "safe zone" to another immediately will probably be unlikely.
In the comics, the group first encountered Abraham when they were back at the Greene farm following the last big battle at the prison. While executive producer Glen Mazzara has said that the TV series has "moved on" and we won't be seeing the farm again, that doesn't preclude a character as important and popular as Abraham showing up.
It likely won't happen the same way as in the comics, though, even if you discount the farm.
The big man was basically the hired muscle for Eugene, a man claiming to be a government scientist who had insight into the root of the plague and a potential cure. Everyone, including Rick and company, gave him the benefit of the doubt for a while, thinking that if it turned out to be true, it was worth helping Eugene.
Of course, it wasn't true--and Rick would know this in the TV series since he spoke with Jenner at the CDC at the end of the first season. That information would significantly change the dynamic of the characters in question and while it's not impossible that Eugene could be brought into the series, he would be pretty transparently walker bait if he were. Bringing in Abraham in a slightly different way without worrying about Eugene and the Quest to DC subplot would allow the post-prison TV series (which we're assuming would be AT LEAST next year if not longer, but still...) to play out very differently from the comics.
The least likely to actually appear in the series, for my money, and for one obvious reason: Randall. Around the same time Jesus first appeared in the comics, Randall appeared on the TV series and had a similar storyline going on. If and when Jesus does appear, they'll have to alter the whole "We're going to kidnap you and hold you to see your safe and then ultimately discuss at length whether we're planning to kill you anyway" thing.
That felt like an instance of something they were doing on the show, that worked really well and Kirkman wanted to use it for the comics. Making the transition back to TV might be pretty difficult to pull off without feeling redundant.
This one would be a bit of a cheat--to introduce Morgan at this point wouldn't really be an introduction so much as a reintroduction. Still, he's a fan-favorite character and he's someone whose name seems to show up on Glen Mazzara's Twitter feed pretty regularly, with viewers wondering when we might next see the man who helped Rick make it through the pilot.
In the comics, Morgan reappeared after Rick and Carl headed to their hometown following Lori's death. The trip, meant to give Rick an opportunity to stock up on ammunition and other supplies using his keys to the police station where he used to work, saw him bump into his old friend again, and Morgan ended up joining the group.