So much about Star Wars is about legacy. The legacy fathers leave for sons. The legacy mentors leave for students. And increasingly, the legacy that one generation of actors and filmmakers leave for younger artists trying to carry the iconic franchise into a new era.

As much as it is an origin story, Solo: A Star Wars Story is also a very clear case of the franchise's focus on passing the torch. A prequel film about the early days of the beloved rascal space smuggler Han Solo, it asks a new actor, the largely untested Alden Ehrenreich, to step into the boots and vest made famous by Harrison Ford, the series' brightest superstar. And in what was at first a practical and then very symbolic partnership, the film's story itself involves an important inheritance, as it was written by the series' most storied screenwriter, Lawrence Kasdan (who goes by "Larry"), and his son, Jonathan Kasdan (who goes by "Jon").

The father-son team spent three years working on Solo, an endeavor that tested and ultimately strengthened their professional and familial bond. And then they spoke about the experience with SYFY WIRE, and offered up new tidbits of information about Star Wars past and present, including insight on Ford's return to the franchise.

Jon, Meg, and Lawrence Kasdan. Credit: Getty Images

Larry, when Kathleen Kennedy and George Lucas first called you in 2012, Han Solo was the project that most interested you, right?

I mean, it was the only one I was interested in, and the wheels did start spinning. There was a moment shortly afterward when we were asked to tell the Disney brass — who didn't own the company when I came on — what we had in mind. It was me and Michael Arndt and Simon Kinberg, and I just told them a very brief little thing about Han being asked his name. I told them his answer and him saying, "I have no people," and the guy who asked saying to him, "OK... Han Solo." And Bob Iger said, "Okay, I'm ready to make that movie."

Then I got pulled away for two years, and then I said, "I can't come back without Jon." He had helped us with Force Awakens at the very end, and then he was brimming with energy where I needed a jump.

How is working as father and son on such a big, sensitive project?

Jon: It's a strange one, you know? Because it's that relationship is fraught. Co-writing is a complex relationship anyway, and to add on to it all of the father/son stuff and then to add on to that Star Wars is so much about generations. It's just very loaded. As Larry said, I was around a little bit for The Force Awakens, and to be sitting on the set with Harrison getting stabbed through the heart by his son.

As Larry and I were about to embark on writing one of these together, it made your head spin a little bit.

Seriously. I hope your arguments were less violent than Han and Kylo's.

Jon: No. That's exactly how I took it to him. I said, "No, she can't say that ever!"

Larry: But he had a mouse instead of a lightsaber.

Video of Solo Red Carpet Premiere: Alden Ehrenreich, Emilia Clarke, Billy Dee Williams & More!

How did you settle disagreements? Because not only are you the father, Larry, you've also been with Star Wars so long.

Larry: I've been with them a long time, and I've collaborated with a lot of different people on not all my movies, but a lot of my movies. It's always difficult at times, and it's always fun at times, and this one turned out to be mostly fun.

Jon: And it ended up being such a long process. It was right when they finished shooting Force Awakens that we started writing this, so we've been on it for about three years. We've worked in different configurations, with me in New York and him in L.A., and both of us in L.A., and then me in London and him in L.A., and us both in London. There have been moments of it that have been hard, and it's been incredibly bonding for us, because to have something like this in common with your father, it's just a very intimate emotional thing.

I know that Harrison thought he should die back in the day. I think you agreed with him.

Larry: I did agree.

So when he did die in The Force Awakens, how did you feel about that?

Jon: Then he wanted to live.

Larry: He had such a good time, I think he was surprised. He got hurt very early on, and we had to re-do everything, and when he came back I've never seen a person more open, compassionate, and generous with everybody than he was through the last two-thirds of that movie. I think when he finally died, he was like, "Really? Maybe I..."

Jon: It was so much fun, and I mean it carried through to literally this morning, when we were with him five hours ago. He's just an unbelievable presence, and his enthusiasm for the movie, I have to be honest, shocked me. Because he was so heartfelt and outspoken and we just... I was expecting a begrudging like, "It's fine."

Larry: The way he embraced Alden and the writing and Ron's direction, it's just been really moving.

Did he talk to you at all during this movie's production?

Larry: He didn't, no.

So he let you do your own thing, didn't feel any ownership.

Jon: I think to some extent, he felt with his death, his ownership of the character was being handed over. I think it was emotional and personal for him, but when he saw how it fit into what he had done, I think he was genuinely surprised and got a kick out of it.

Video of Watch Harrison Ford Surprise Young Han Solo Alden Ehrenreich During ET Interview (Exclusive)

Larry, you wrote Han Solo, the character — your favorite character — about 40 years ago now. And we didn't know anything about him back then, just that he was a smuggler.

Larry: That's what really got me about him. It was what George had written in A New Hope, in one of the great scenes in all of movies. The cantina. What's great is it's so economical. It tells you a million things at once. You get the whole flavor of Han's personality and his relationship to Chewie. You see something in Ben Kenobi that you have not yet seen, which is that he's very incisive about the lie that Han tells him. He's mentoring Luke at that moment, and then you see Han shoot first.

You say he shoots first.

Larry: Yeah. Absolutely.

When you were writing for him for Empire and Return of the Jedi, in your mind, was there a backstory that you cooked up so you could write him better?

Larry: No, I was writing from A New Hope on and as I say, to me the cantina tells you everything you need to know.

Jon: But little subtle things, like the first exchanges with Lando, ended up informing this movie in ways that I don't think Larry quite imagined he would have to contend with.

Larry: Things like when they greet each other, the way he's wary of Lando, the way that Lando immediately focuses on Leia. It's all in this movie.

And so much backstory has been created since, in comics and novels and video games. You worked with the Story Group on Force Awakens, so did you work with the authors of the comics and the books for this?

Jon: No. With this movie, because of Kathy's relationship with Larry and because of what Larry brings to Star Wars -- he's more than just someone who had written the best one, he was the continuity between what George had done early on and what Disney was hoping to do. He brings us so much authority and strength that we were really put in a situation where we were allowed to go into a room, use the Wookieepedia — which we used relentlessly — and craft the story we wanted to craft. We figured out what we thought would be the most satisfying and delightful version of a western with this guy at the center of it.

Larry: Because that's what he struck me as in the cantina. There couldn't be a more classic gunslinger than the way he is there. I've always been drawn to film noir and to crime shows, crime movies, and Jon was so on that because he shared that enthusiasm.

Video of Star Wars cantina scene

In this movie, Han has to go on a hero's journey of some sort, but he also has to do that in A New Hope, transforming from cynical to at least somewhat of a team player. So he can't leave Solo as a fully formed character. How'd you approach that?

Larry: You know, it's funny, because that phrase has not come up once. I've heard it ad nauseam for the other movies. There's an antithesis to that. That's the journey he goes on. He goes on a rogue's journey. He really learns how he can't trust anyone and that if he is the straight shooter in the group, it's probably not going to work out.

Jon: And what we did talk about a lot was, if the character you meet in Mos Eisley is this Bogart-esque, wears cynicism as an armor around a very, a thumping, beating heart of love and warmth, how did he get that suit of armor? And what are the events that put that armor around him? Part of the design, admittedly, of this movie was that you'd only see some steps of that journey. There are more on the way to Mos Eisley, and he isn't that guy yet.

Do you guys want to write more of that journey, more of these movies?

Jon: I would love to see those more. We love this story, and what we were saying just recently was, we both feel like Alden earned his bones in this movie as Han, and by the end of it you're with him. And I don't think that's an easy accomplishment, and once you have, you sort of think, "Okay, well, I'll take some other rides with you." And Chewie doesn't need to earn any bones. The moment he shows up on screen, he's Chewie again.