Director/producer Todd Phillips during the filming © 2010 Warner Bros and Legendary Pictures

Director/Screenwriter/Producer Todd Phillips’ 2009 movie The Hangover became the highest grossing R-rated comedy of all time and won a Golden Globe for Best Motion Picture – Comedy or Musical.

His new comedy Due Date reunites Phillips with Zach Galifianakis, one of the stars of The Hangover. In this film he portrays Ethan Tremblay, a lonely and annoying man who is traveling with is dog, Sonny. He meets Peter Highman (Robert Downey Jr) on a plane from Atlanta to Los Angeles, and manages to get the both of them thrown off and put on the no-fly list. Desperate to reach LA in time for the birth of his first child, Peter is resigned to hitching a ride with Ethan and Sonny, on a road trip that will be unforgettable.

Due Date isn’t just funny, there are tender moments in this too, was that really important to you?

Barry (Director/producer Todd Phillips), Heldi (Juliette Lewis) and Ethan Tremblay (Zach Galifianakis) © 2010 Warner Bros and Legendary Pictures

Oh yeah, I think we wanted this to operate on two levels, obviously the comedy is a huge part of making a comedy and then we really wanted to connect emotionally. Robert jokes with me about why Due Date is better than The Hangover. He says, ‘It’s because Due Date is about something.’ Which I think is an interesting way of putting it, but I know what he means.

How did you know that Zach and Robert would have the right kind of chemistry to make this film work?

People always cite chemistry in these kinds of movies. They say it’s the chemistry between the two lead actors that makes it work. I believe what makes Due Date work is anti-chemistry; it’s two guys with zero connection and zero rapport, constantly butting heads, that generates both the tension and the comedy.

Zach is always annoying, and Robert’s cool. When we first got together, Zach and I went to Robert’s house for dinner. This was before Robert agreed to do the movie. We were just going to talk about it. And Zach came over and immediately made this comment about an ex-girlfriend of Robert’s that Zach didn’t know was his ex-girlfriend from years ago. It was a really rude comment, he put his foot in his mouth instantaneously in a very Ethan Tremblay way. And I thought right there, ‘Okay, this could work.’

Is Ethan’s character too annoying?

Robert Downey Jr, Zach Galifianakis and Director/producer Todd Phillips © 2010 Warner Bros and Legendary Pictures

Honesty, innocence and a humanity makes you connect with him and root for him despite it all. Ethan is a complex character. He has just lost his father, who was his best friend, and is having a tough time dealing with that. There’s an underlying desperation in everything he does and an eagerness to please to the point where just making friends means trying too hard.

What does Zach and Robert bring to this movie?

Zach brings a sense of spontaneity and danger and I think comedy is best with an undercurrent of danger so that you never know exactly what’s going to happen or what someone will say or do. In that sense, he’s the perfect comedic actor.

Not only is Robert a world-class actor but he’s naturally funny. I wouldn’t think of casting Robert Downey Jr. as anyone’s straight-man. In Due Date there is no straight-man because they’re both screwed up in their own ways. And the beauty of Zach and Robert playing off each other is that they’re both funny, but their humor comes from such different places and their styles are so different that you’re not mining the same vein.

When you let them go and they get in this car together, is there a lot of ad-libbing?

Robert Downey Jr, Zach Galifianakis and Director/producer Todd Phillips © 2010 Warner Bros and Legendary Pictures

It’s not even so much that we improvise on any of these movies; it’s that we talk about it for hours every morning before we shoot so in a weird way we rewrite that morning. So it’s not so much that the cameras are rolling and you just let them go, which of course I let them do as much as possible, but that’s not even where the energy comes.

Robert’s genius comes in really dissecting the script and really taking apart what’s important, what’s needed, and more importantly what’s not needed and what can go unsaid. He’s best when he’s heard and he’s part of the process and not just a guy for hire. And for me it was my best experience as a director, just working with somebody like Robert because every morning he just blew my mind.

Why do you think road trips make great fodder for comedy films?

Director/producer Todd Phillips during the filming © 2010 Warner Bros and Legendary Pictures

I think it’s because your characters are out there without a safety net, that’s kind of the simplest way to explain it. When you leave your community, your home, your friends and family are not with you and you’re flying without a net, and I think that makes it (funny). The essence of comedy is conflict, and I think that makes for a lot of conflict and tension.

There’s something about a road trip that brings out the extremes of human reactions and emotions. It’s a great opportunity for surprises and for people to learn things about themselves or each other that they’d never see if they weren’t being pushed to their limits, or having to make the kinds of quick, instinctive decisions you have to make on the road. No matter where we are in Due Date, no matter what kind of chaos they’re going through, it all comes down to these two guys working out their issues.

Judy Sloane

Judy is Film Review Online's regular Los Angeles based reporter.