Stephen King is one of the best-selling authors of all time. His stories reach audiences around the world and across decades, and yet, adapting his work to cinema has proven a challenging task over the years. Usually, something vital is lost in translation. And among his epics works like The Stand and The Dark Tower, which have proven among the most challenging to adapt, IT is one of King's most ambitious and beloved tales; a 1000+ page opus of coming-of-age in the face of consummate evil.

It should be no surprise then that the IT adaptation has had a journey of its own. First set up as a Warner Bros. project with Cary Fukunaga attached to write and direct, the project moved to Warner's sister company New Line after Fukunaga departed over creative differences. Enter director Andy Muschietti, his creative partner (and sister), producer Barbara Muschietti, and screenwriter Gary Dauberman, who built from the existing script to create the film we have now -- a bonafide horror hit in the making that's already breaking pre-sales records and is firmly on track to follow suit with box office records. Producers Seth Grahame-Smith (Abraham Lincoln: Vampire Hunter) and David Katzenberg (The Goldbergs) have been aboard the project through it all, a six-year ride to their feature producing debut.

With IT arriving in theaters this weekend, I recently sat down with Katzenberg and Grahame-Smith to chat about the film and their plans for the sequel. We talked about how the project evolved from Fukunaga's draft and how the Muschiettis transformed it to the film we see now, bulking up Beverly Marsh's character and finding a star in the making in young actress Sophia Lillis, and the evolutionary process of bringing Pennywise to life on the big screen. We also talked about where they're at in the scripting process for the sequel and a whole lot more. Check out the full interview below.

Talk a bit about how long were you guys have been involved with the project. Did you participate through both directors and that shifting evolution?

SETH GRAHAME-SMITH: Oh yeah.

DAVID KATZENBERG: Yeah, I mean it's a little over six years now that we were brought in by Dan Lin and Roy Lee, who had the rights to the property, and we've been along for the entire ride. Which makes it even more special now that we're actually here. But we were involved in the first version with Cary, and Cary gave us a fantastic script, and we were around for finding Andy and his sister Barbara and yeah. So the whole journey.  

The Fukunaga and Chase Palmer script is out there, it's very clear that the backbone of that script is still a big part of the film.

GRAHAME-SMITH: Oh yeah.

KATZENBERG: Oh yeah.

GRAHAME-SMITH: No question.

What do you think is the key thing that Andy and Barbara brought in that took it and brought it to the final form we see now?

GRAHAME-SMITH: For us, it came down to somebody who wanted to capture the tone of the book. I mean the Stephen King tone of... you know it's a mix of sentimentality, and coming of age, and pure unbridled horror, and there's an undeniable sexuality to the story. Chase and Cary obviously captured that in the script, with things though it comes down to if everyone's not exactly on the same page with every single detail, you know, sometimes it doesn't work. We are incredibly grateful to Cary; he and Chase wrote an incredible script. Gary Dauberman did great work, you know, sort of changing it suit Andy's tone a little bit more.

And I think that, for us, when we met with Andy, the first time we met him he came in and started talking about the kids, and he started talking about what the book had meant to him when he was a kid growing up in Argentina, and being a Stephen King fan. And to us, that's the way into, at least this first chapter, is you have to understand this is really all about these kids being kids in Summer of 1989 and going through something alone that is terrifying and invisible to most adults.

And so the thing that was crazy for me when we were making the movie is that I was 13 in the Summer of 89, and I did grow up in New England, and I was reading Stephen King when I was 13 in the Summer of 89. So for me seeing those beats come to life, in a way that related exactly to where I was in my life, was crazy. I mean, I've said this before, one of my small contributes to The Losers Club, was when we were getting ready to start shooting I put together a sort of bible of, these were the shows I watched on T.V that Summer, these were the movies I was excited about that Summer, this is the album I bought near the first CD that I bought because I knew that Andy was going to let them riff so much and improv, these kids were all born in 2002. Which is absurd to say.

It's upsetting. 

GRAHAME-SMITH: [Laughs] Right.

I'm always curious about how a film evolves, especially a film like with such massive source material, how much you guys shoot and what it was edited down to. Are there a lot of deleted scenes? 

KATZENBERG: There's not too many deleted scenes, I mean obviously there was stuff that was cut to bring it down to time, but nothing that super -- not a whole scene or something that's super drastic that I think that anyone would really miss, to be honest. I think we spent so much time figuring out what parts of the book we wanted to be in the movie, and also knowing we were breaking it down into two parts, that there really wasn't room to cut something massive out of the film.  

GRAHAME-SMITH: Yeah, I mean our schedule is also pretty challenging, to begin with, just because of the fact that the stars of our movie can only work a set number of hours a day. We can't do overtime with the kids, and they also all have to take breaks to go to school every day, even though we were shooting in the middle of summer. You know, we had to take all that into consideration, we had to be really judicious when it came to editing the script down before we went in. So there's not a lot of chaff on the floor. There's a couple of things that maybe we trimmed significantly.

KATZENBERG: It's more exposition and transitional stuff, and you know, but nothing ...

GRAHAME-SMITH: Nothing outside the ordinary. It's not like we, to your point, like as King fan, we didn't like, shoot The Black Spot and then say we're not going to do it in the movie.

And I would imagine with the scares and that kind of stuff, anything with prosthetics and effects has to be so storyboarded... 

GRAHAME-SMITH: Yeah.

KATZENBERG: Yeah. 

So most of those probably remain intact in the movie, right?

KATZENBERG: The schedule for this movie was nuts. It was extremely, extremely difficult, and everything was extremely well thought out and planned before.  

GRAHAME-SMITH: Because you know, and you having seen the movie, it's like... We went in saying, this has to feel bigger than your average horror movie. It's got to have more scope. It's got to feel like a bigger movie. And by the way, we were on location for seventy percent if not more of the time. This wasn't a movie that was all shot of stages, we finished on stages at the end.

KATZENBERG: Yeah it was location, it was Toronto during the summer, and it was hot and humid.  

GRAHAME-SMITH: Yeah.

Oh my god, yes, it was really hot!

GRAHAME-SMITH: You're remembering that, right?

Yeah, I do actually.

KATZENBERG: It was very hard to stay dry there.  

GRAHAME-SMITH: Right.

KATZENBERG: Luckily the kids were running around so they could be sweaty.

A sequel's not officially announced yet, but it's at the end of the film the end credit tag is... 

GRAHAME-SMITH: Sure.

It's "Chapter One". 

GRAHAME-SMITH: Sure, yeah.

So knowing that you have kids that are at a very dangerous age of rapidly growing up, where are you guys at in your production scale and how quickly are you trying to fast track this? 

GRAHAME-SMITH: Well, the first thing I would say is, you know, there's nothing official about a second part yet. And I'm not saying that just to be coy, it's just the way it is. The movies going to come out and then we're going to make a decision.

KATZENBERG: We've obviously put thought into it.  

GRAHAME-SMITH: Right, yeah.

KATZENBERG: But really at this point that's really it.  

GRAHAME-SMITH: Yeah, I would say, we have thought about it, we have talked about that issue.

KATZENBERG: Especially in regards to beats in the first film and how they may be affected in the second film.  

Right, and Andy has always said he wants to have a dialogue between the two timelines. So, you don't want Finn Wolfhard to suddenly look like he's a linebacker or something.

GRAHAME-SMITH: Right. Although it depends on which character is having the dialogue, and which character you know, ages perhaps differently from other characters. We ran into the issue of, we did just a little bit of additional photography earlier this year, probably like what? February or March?

KATZENBERG: Mm-hmm.

GRAHAME-SMITH: And in the time between wrapping in September and February and March, like Finn and Wyatt looked, they were a foot taller each.

KATZENBERG: What was more drastic than the look was their voices. Even Jaeden, his voice got extremely deep. 

Do you have a script at this point?

GRAHAME-SMITH: It's being worked on, yeah.

Gotcha.

GRAHAME-SMITH: Yeah, so the scripts being worked. We obviously want to be ready when we get the word.

Exactly.

GRAHAME-SMITH: We don't waste any time, we want to jump right into it when we get the word. But we haven't gotten the word yet.

KATZENBERG: There's no word yet. 

GRAHAME-SMITH: There's no word.

KATZENBERG: And we're not just saying that, there really isn't.  

No, I'm not scoffing like I don't believe you, I'm scoffing like … just wait til' the box office comes in because I think you're going to be just fine. 

GRAHAME-SMITH: Yeah exactly, exactly.

It's tracking beautifully.

GRAHAME-SMITH: It's fine, but then who knows.

Yeah, never count your eggs. 

GRAHAME-SMITH: We're superstitious guys.

Totally, and I understand why, but it's a really good movie I think it's going to be huge. 

KATZENBERG: Thank you, thank you.  

In Chapter One, something I really loved about the film was the attention paid to Beverly, and for me, she's kind of secretly the lead character in this ensemble.

KATZENBERG: Sure, yeah.  

How did that evolve in the script? She even gets some of Bill's big moments towards the end. And then can you talk about finding Sophia, because she's ridiculously good. 

GRAHAME-SMITH: Yeah sure. So Sophia was, I think for us, the easiest piece of casting.

KATZENBERG: Yeah.  

GRAHAME-SMITH: We saw a lot of great actors, young actors, actresses. Great! There is just something unique about her, that jumps right out at you. She holds the screen in a way that few people her age can hold the screen. She's a star. We said it from the minute we saw her. And by the way I think we have a lot of stars in this movie, but ...

KATZENBERG: I remember though, I think we saw her audition on tape, not in person.  

GRAHAME-SMITH: Right.

KATZENBERG: And we were both, I think, huddled over his computer, and ...  

GRAHAME-SMITH: I remember it!

KATZENBERG: And instantly ...  

GRAHAME-SMITH: We were like, that's a star! You can just feel it. And you know, she's a very sweet, very shy girl in real life, but when she turns it on, she's electric. So you know, you need that because she is... Andy was adamant that she is -- and I think this is clear in the book too for anyone who's read the book, she is the glue that binds together the Losers Club. And, of course, we're not going to do the Ritual of Chüd, and she's not going to bind them together in that way. Fine. But she needs to the spiritual, emotional core of the group. And so, if the Losers break up, what's the one thing that's going to bring them back together. It's sort of the question that was posed, and why we honed the third act of the movie that way and gave her those moments. And also, once to get to know her, you want to see her go one on one with Pennywise, you know, you want to see that happen. So finding her was really for us, it was a no brainer. I think most of the kids were that way.

KATZENBERG: Yeah, we saw thousands of kids but I think we knew instantly.  

GRAHAME-SMITH: No, with her it was instant.

Yeah, she's incredible. And as I mentioned, I visited the set and got to talk with her there. And it's like you said, she's very sweet, she's very shy, so when I saw the movie I was like, "Oh holy shit, girl, I did not realize!" 

GRAHAME-SMITH: She's a badass.

And of course, there's Pennywise.

GRAHAME-SMITH: Yeah sure.

I just realized all my questions to day have been focused on the kids because they kind of steal the movie. 

GRAHAME-SMITH: Yeah! Yeah, yeah.

Everyone's going to go for Pennywise but they're going to want to come back for the kids.

GRAHAME-SMITH: That's what we hope, best case scenario.

KATZENBERG: I love the idea that people pleasantly surprised by with the Stand by Me [element] of our film. 

So with Bill, and the way Andy worked with Bill, do you feel like their take on Pennywise was something they had in mind from the beginning? Or was there an exploration process? 

GRAHAME-SMITH: I think it was an exploration, without a doubt.

KATZENBERG: It evolved.  

GRAHAME-SMITH: Without a doubt. I think the thing that we all knew, including Bill and Andy was, look we have to respect and honor the Tim Curry performance, but we can't do that. That is iconic, you're not gonna top that version of it. You know, how do we do something unique that also feels iconic but feels different. And so that's a big challenge. You know Bill was I think 24 when we started like the process, incredible right?

Crazy.  

GRAHAME-SMITH: And he just, casting him, we were talking about his earlier, he can do things with his voice, and with his body, and with his face that are phenomenal.

Truly. 

GRAHAME-SMITH: And he inhabited that character.

KATZENBERG: And in terms of the look too, I mean, we have to give Andy obviously a ton of credit because Andy from the very beginning, we'd go to these meetings with him and he'd be sketching this stuff on his pad. And we didn't know what it was but it was like this horseshoe, and that slowly evolved into the mouth. 

GRAHAME-SMITH: The smile going to the eyes.

KATZENBERG: The smile goes to the eyes. I remember the first time seeing that unscripted, it literally was just like a horseshoe.  

GRAHAME-SMITH: I should have grabbed that script page.

KATZENBERG: And it just kept evolving...  

GRAHAME-SMITH: Yeah.

KATZENBERG: And Andy really kind of sketched and drew the look. I think in terms of Bills mannerisms, and his voice and his face.  

GRAHAME-SMITH: The way the schedule worked out too, the shooting schedule, Bill was in Toronto, but we didn't really start shooting with him until a month in. Even while we were shooting, Bill was refining and experimenting, and working with Andy.

KATZENBERG: And the kids did not see him until they shot with him.  So they didn't know what Pennywise was going to look like until, on the day. 

GRAHAME-SMITH: The first scene was in the kitchen.

KATZENBERG: It was pretty awesome.  

GRAHAME-SMITH: And evil. When he's stalking over Eddie.

KATZENBERG: Everyone was extremely frightened.  

GRAHAME-SMITH: We were. Because you know Bills tall, but with the boots he's like 6' 5" and, just him walking around in that makeup, it took us a couple of days before we could like settle in because you don't know, like, does he want to be talked to? Does he not? And then you realize ...

KATZENBERG: It was cool, and it worked well because I think the kids were genuinely frightened.  

I didn't know that was the first scene, and that makes total sense having seen the film, because the energy in that scene is so intense.  

GRAHAME-SMITH: There's a lot of drool in that scene.

Yes, there is! 

GRAHAME-SMITH: Yeah.

They said his teeth caused him to drool, right?  

GRAHAME-SMITH: Well I don't know if it was that or that might have been a choice. But what I love about our kids, our actors, is like, Jack spit right back at him in his face, like he was getting drooled on, and spit right back at him and like, wasn't backing down.

Oh man, that's fantastic. Yeah, those kids are... they're great. I imagine there was lot of improv with that group.

KATZENBERG: Yeah. 

GRAHAME-SMITH: A lot.

KATZENBERG: On and off the screen, I mean, the instantly became best friends, they still are, I'm sure you've seen them, they literally do everything together. And one of the coolest things about the film is, I think their relationship and their dialogue, and a lot of that was them kind of, from knowing each other, you know there was definitely improv and ad lib. And they definitely, I don't know, it was crazy, their relationship kind of grew over the Summer of us filming on and off the screen, which was incredible to watch.  

GRAHAME-SMITH: Yeah, and that's, I sound like a broken record because I'll keep saying it until the day I die. But we got so lucky in that we found these kids who were individually great actors, fine. But when they came together, there was something about their chemistry off screen that made them become, like thick as thieves off screen, they are best friends, BFF's for life, if they were older they would have done the Lord of the Rings thing and all got the same tattoo. I mean they are, they'll run into each other twenty years from now and pick up where they left off and hug each other because they had that kind of bond over this very sentimental Summer in their lives, 13 years old. Like they slept over at each other's place. And they spent every waking minute gossiping and laughing and pulling pranks together, and you feel that when you watch the movie.

KATZENBERG: All you have to do is go to any of their Instagram's and you'll see ...

GRAHAME-SMITH: Oh my god, yeah. They're still to this day ...

KATZENBERG: They're inseparable.  

IT opens in theaters nationwide on September 8.