By any standards, you have to consider him a major movie star, yet whenever I've had a conversation with him, he's one of the most normal, casual guys I can imagine. Someone like George Clooney has a sort of aura where you are constantly aware of the reactions of everyone around him, where even if he's not trying to turn it on, he creates this ripple just by walking through a room. I honestly believe Damon could get away with relative anonymity if that's what he wanted. He's certainly able to turn up the wattage for the films he's in, but in person, he strikes me more like a dad I'd meet at a Little League practice than a movie star selling a $100-million-plus production.
One thing I've heard repeatedly from people who have worked with Damon is that he's a great collaborator, willing to put the film's needs above his personal needs. There are plenty of actors who will ask for changes that are about their image or their public persona, but Damon seems like much more of a big picture guy, someone whose goal is always to make the film better overall.
All in all, however, Damon is in good spirits. Only a couple of weeks earlier, he had renewed vows with his wife of eight years, Luciana Barroso, in the Caribbean. And just last night - perhaps a clue as to why he's clutching that caffeine - he'd danced the night away with Luciana, Channing Tatum and "a lot of tequila".
As Elysium director Neill Blomkamp puts it, Damon is unafraid to "damage his brand".
"I never thought of it that way," says Damon, sporting black-rimmed glasses and salt-and-pepper hair to rival that of his old mate, George Clooney.
"I remember talking to this Japanese golf pro once and he told me the thing about a golf swing is, at the top of your backswing you have to say 'What the f---!' - you have to just let it go. Because if you try to control it, you'll ruin it. I thought that was good advice for a career in the movie business. It's impossible to micromanage an image, it's impossible to control your career. So it was always just a matter of trying as many varied types of projects as I could."
He unbuttons his sweatshirt, takes up the sleeve of his T-shirt and shows me, just below the right bicep, written italics. Lucy, his wife's name. "I've got her, she's got mine. One morning Lucy told me: "Don't you think we should have a tattoo?" And what could I say?"
Clooney says the film offered something rare in the canon of World War II films: an untold story.
Heslov says that while the pair wanted a break from their past work, those projects, which include 2005's Good Night, and Good Luck, opened the door to getting an A-list cast, composed mainly of friends. Clooney's co-stars include Matt Damon, Cate Blanchett, Bill Murray, John Goodman and The Artist's Jean Dujardin.
"When we write movies now, we usually have specific friends in mind," Heslov says. "It's nice to be able to call them and say, 'Hey, we have a new movie. Want to come spend a few months with us?' Usually, it works out."