ATLANTA — Forget Mac’s absurd weight gain, the meta insanity of Lethal Weapon 5, or Guillermo del Toro’s turn as glass-eyed Pappy McPoyle. The most shocking moment in It’s Always Sunny in Philadelphia history came during the Season 12 finale when, as the gang all shook their butts along to Malow Mac’s “County Jail,” Dennis had a revelation: I can’t do any of this shit anymore. I’m leaving. I’m gonna go be a Dad.

And just like that: Dennis Reynolds quit the gang.

The sudden departure of Dennis, played to creepy perfection by Glenn Howerton, left Sunny fans with plenty of unanswered questions. Is the divorce permanent or will he be back? Why did he leave? Did it have to do with his new series, A.P. Bio? After all, Howerton not only starred as Dennis, but also served as a writer and executive producer on the long-running FXX sitcom.

I’m seated across from Howerton at the Four Seasons in Atlanta. He’s here with the cast and crew of A.P. Bio for aTVfest, a television festival hosted by SCAD, where the NBC show is having its world premiere.

Created by SNL writer Mike O’Brien and produced by SNL’s Lorne Michaels and Seth Meyers, Howerton stars as Jack Griffin, a big-headed Harvard philosophy scholar who, after losing out on a cushy professorship, is forced to move back to Toledo and teach high school A.P. Bio. There, the school’s pushover principal (Patton Oswalt) and his not-so-impressionable students clash with Jack, who seems far more interested in trying to get laid than in imparting knowledge.

The Daily Beast sat down with Howerton at aTVfest to discuss his new show, why he walked away from Always Sunny, and much more.

There’s a heck of a team behind A.P. Bio, with Lorne Michaels and Seth Meyers on as producers and Mike O’Brien as creator. Is that what attracted you to the show?

It was all of it. The first thing was the script. I wouldn’t have been interested if I hadn’t read the script and loved it, so that combined with the fact that I was familiar with Mike’s work on SNL and was a fan of his, and then of course having Lorne and Seth involved, especially meeting with Lorne and talking about it, I felt he was going to protect the integrity of the show and that we were going to be able to make something that felt different.

“ Look, it’s going to be hard for people to see me as anything other than Dennis. That’s the blessing and the curse of playing a character like this. ” — Glenn Howerton

What reassurances did Lorne give you?

With somebody of his status and someone who’s as busy as he is, I don’t trust that they’re going to actually be that involved. And I don’t know Lorne. He’s got a great reputation, people like him, and he’s done a lot of really great stuff, but again, you never know. But when he was talking about it, he had such an intelligent take on what the show is, why he liked it, what he thought was funny about it, and why he liked me for the role. It made me feel comfortable that we were on the same page about what makes the show funny, what makes it tick. Knowing that he and I were on the same page creatively, and him assuring me that, from a business standpoint, he was going to fight as hard as he could to make the show that I actually read and that it wouldn’t be watered down, that was reassuring. And that’s not a comment on NBC, that’s a comment on what can happen to any show at any network if you don’t have creative control. Things can get pushed in a direction that is not what originally made it great.

Was it difficult for you to surrender creative control and give yourself over to someone else’s project? You’ve had such a big hand in all things Sunny.

It was extremely scary, and that’s why it was important for me to talk to Lorne about it and to sit down with Mike a couple of times. After meeting with them, I felt that I could relinquish control and let them steer the ship. In talking with Mike, he has such a confidence about his sensibility and what he wanted to accomplish. It’s important to me that if I’m not going to be in control, I need to have someone in control who has strong opinions—even if we disagree. And sometimes we did. But I was happy to disagree with someone like Mike because he was collaborative, took my opinions very seriously, and stood his ground. I like that.

These characters—Jack Griffin on A.P. Bio and Dennis Reynolds on Sunny—are similar in that they’re both legends in their own minds.

That’s a perfect way of putting it: Legends in their own minds. Initially, my goal was to go out and do something completely different than what I was doing on Sunny, because it’s important for me to be able to express myself creatively as an actor in a variety of ways. Fargo was a comedic character, but a completely different comedic character. In many ways, this character on A.P. Bio didn’t fit the mandate that I originally set out to do, but it was just so good. It felt like I put on a suit that was already tailored to my body. It was exactly my sense of humor, and I couldn’t say no. The temptation was too strong.

Did turning 40 have anything to do with it? Where you maybe thought about needing a change in your career and walking away from Sunny?

It’s possible that had something to do with it. I never had any “I’m turning 40” kind of crisis or anything. I can’t think of a more creatively satisfying job than It’s Always Sunny in Philadelphia. I got to express myself creatively in ways that I never thought I could—or would. I never set out to be a writer or even a producer, and to get to create something whole cloth like we did with Sunny was an absolute dream, and to have people respond to it the way they did. We made something very pure; it was exactly what we wanted to make.

So why did you leave?

I think after being on the show for 12 years, it’s not a knock on Sunny, you just want to branch out and do other things. I saw other people going off and doing other things. The thing that makes it difficult, for me, is that I struggle to identify as a comedy actor because I never set out to be a comedy actor. So sometimes I clash with my old self that wanted to be an actor that does all kinds of roles. The younger version of myself is constantly in conflict with the version of myself that became known for this one character and known specifically for comedy. I love comedy and think I have a knack for it, but it’s…weird. Originally, I wanted to do drama. So it wasn’t necessarily turning 40, but I think it was just changing and developing as a person, and wanting to do new things.

I’m a longtime Always Sunny viewer, so I’m curious how you all arrived at the idea of Dennis leaving the gang?

You know… there was a revelatory moment that we had shooting Season 11 where we had Mac come out of the closet during the cruise-ship episode, and by the end of that two-part episode he goes back in. We wanted him to genuinely come out of the closet, and then once he could justify going back in, he went straight back in. I always thought that was funny—and continue to think it’s funny—because it’s so… sad. There are so many people who hold themselves to a religious standard and to a societal standard that they sadly no longer really have to hold themselves to, but they feel this pressure to. In Mac’s case, he feels this pressure to [conform] because he has something against being gay and he doesn’t want to be gay.

With Mac it seems like it’s due to his religious hang-ups.

It is mostly a religious thing. And for as awful as our characters are, we’re always encouraging him to come out of the closet, because we don’t care if he’s gay or not. We all already know and don’t give a shit. In pure Sunny fashion, our spin on that is, “Look dude, we dislike you either way. The fact that we dislike you has nothing to do with whether you’re gay or not, it has to do with your personality.” But all that is to say, we got quite a big reaction from the fans, which we listened to, and I think it was important, ultimately, to have him come out of the closet because I think it was important to send that message to the community, and we also wanted to change things up and put new obstacles in the characters’ lives, both to keep things interesting for ourselves and the audience. Part of that was having Dennis leave at the end of Season 12. We wanted to do something a little bit different, a little bit shocking, and also have a big, emotional moment.

Did it have to do with the cultural climate at all? Dennis is a character who, because of the chaos and messiness of the show, gets away with a lot. He’s essentially a rapey, pickup artist-type when it comes down to it.

Umm… I do think that it’s time for that character to change. I think he has to change. It was never really acceptable the way he behaved, and now it’s even less so in terms of how you actually can’t get away with it anymore. Before, you could kind of get away with it and skate by, but you can’t skate by anymore—and I think that’s a really good thing. You shouldn’t be able to behave that way. And for people that understand our show, it was always our intention to show that he doesn’t ever get away with this behavior. He’s not in jail but he never wins, he never succeeds, he’s never glorified.

He does seem fairly miserable.

I think he’s maybe too narcissistic to be miserable. He’s angry, defiant, and petulant, but I don’t think he’s sad or anything.

Why do you think you’re so good at playing these vainglorious characters who are, like we said before, legends in their own minds?

You know what? I like to think that in real life, as a person, I strive to be good, try to be aware of the effect I have on people around me, and try to be a socially-conscious person. I’m fascinated by people who are not that way; people who don’t give a shit about anybody but themselves. A lot of comedy comes from anger, too. The comic mind, we have a tendency to observe what goes on in the world and need to comment on it; there’s a burning desire to vent. If we didn’t have that outlet, we’d be angry people all the time. So I have to skewer it, satirize it and find the comedy in it just to survive, because I get really upset by people who are completely self-centered and narcissistic. It’s interesting, then, to try to get inside the head of someone who doesn’t give a shit about anybody but themselves and try to find out what’s funny about that. It’s a release valve for me. But I don’t know why I’m good at it. From a very young age, I think that I’ve possibly had some anger issues, and I feel I can let it out through these characters.

One of the things I’ve always enjoyed about Sunny is all the real-life couples on the show. There’s Rob and Kaitlin, Charlie and Mary Elizabeth (aka “The Waitress”), and you and Jill, who appeared as your victim in the infamous “D.E.N.N.I.S. System” episode.

Charlie and Mary Elizabeth were together before the show started, Rob met Kaitlin on the show, and Jill and I were already together. We’d been dating at that point for two years. I’d wanted to do it with her, because as a person I felt weird about doing that with someone else—and not doing it with an actress that fully trusts me. The other reason, too, is that we felt like she was right for the part because she’s so funny and smart, so I didn’t really want to do it with anybody else.

Have you two re-watched the episode recently?

[Laughs] I haven’t seen it in a very long time. It would definitely be strange to see it today.

Playing an iconic comedy character like Dennis Reynolds, did you find it difficult to book other gigs? To have people see you as anything other than Dennis?

You know, I don’t know if I’ve lost out gigs because people couldn’t see me as anybody other than Dennis. I say to my agents a lot, “I get it, it’s going to be hard to get out of this,” but then they say that when they talk to people they can tell I’m a good actor. Look, it’s going to be hard for people to see me as anything other than Dennis. That’s the blessing and the curse of playing a character like this. But I don’t mind that challenge. I look forward to surprising people with what I can do.