TORONTO—There are a couple of telling signs that you’re in the same room as a bona fide movie star. One, a publicist preludes the actor’s entrance with a strict reminder to nix any questions about his upcoming appearance in the new Star Wars film. Two, the all-star ensemble in his latest feature, This Is Where I Leave You (now playing)—which includes heavyweights like Jason Bateman and Tina Fey—all move their schedules around to accommodate the guy. Two years ago, this particular star was a supporting player in an HBO series, originally auditioned as “Handsome Carpenter”. He was just out of acting school, before which he was fresh out of the military. Now, he’s getting Jane-freaking-Fonda to revamp her calendar so it works for him. Such is the life of Adam Driver.

Since starring in Girls as the unpredictable, animalistic Adam Sackler, Driver has ironically enjoyed more success than any female on the show (creator and star Lena Dunham runs a close second), as he’s become a bankable heartthrob bursting with potential in the eyes of studio heads. So much so that Where I Leave You director Shawn Levy felt it was absolutely necessary to get Driver, whom he calls “this beast of an actor”, to play Philip, the youngest member of the dysfunctional Altman family.

“I was doing Girls while we were doing this movie,” says Driver in a hotel-room interview. “It wasn’t working because of scheduling, but Shawn called Jason and Tina and asked if they’d be willing to shoot on weekends to accommodate the schedule shift and they said yes. And for me that was a huge thing. I was very moved by them being able to make it work.”

As for Driver’s personal life, it’s tempting to believe that he’s very similar to his Girls character. It’s the introduction most audiences have had to the actor and they do have the same first name, after all. But the 30-year-old, who has two other films at the Toronto International Film Festival (the Noah Baumbach–directed While We’re Young and Hungry Hearts, for which he won best actor at the Venice Film Festival), has a concentrated seriousness about him that one can’t help but think is a product of his time spent in the Marines.

“Well, that was a different time in my life, when I had just come out of the military. So I was, uh, readjusting to being a civilian again,” says Driver, when asked about a recent GQ cover article in which he admitted to making fellow students cry at Juilliard. “Believe it or not, being in the military is very different from being in acting school. I grew up fast in a way that suddenly you were responsible for things that aren’t typical for 18- or 19-year-olds, people’s lives and things like that. And it just ages you in a way, I think, that when you get out and lead your civilian life again, you want to do things that you took for granted.”

Driver continues: “There was a big learning curve of how you adjust to being a civilian again, and it’s not appropriate to yell at people like that, and people are people, and I can’t force my military thinking on them.” He pauses, and then chuckles. “I think I’m better adjusted now.”