Ben Stiller's comedies have collectively made billions yet, in person, he has the air of a man who would rather stick needles in his eyes than crack a joke. This business of comedy is, apparently, very serious. In truth, his humour has never been borne out of repartee or goofiness: it owes more to self-conscious neuroticism or earnestness, as his greatest film triumphs – which include Zoolander, Night at the Museum and the Fockers trilogy – demonstrate.
Stiller is currently co-starring with Vince Vaughn, Jonah Hill and Britain's Richard Ayoade in the sci-fi satire The Watch, familiar comic turf for an actor who first hit career paydirt with There's Something about Mary in 1998. The son of veteran comedians Jerry Stiller and Anne Meara, he'd been paying his comedy dues with modest success for more than a decade prior to Mary.
He has been a frequent collaborator with his comic peers Will Ferrell, Jack Black, Owen Wilson and Vince Vaughn. The Watch reunites him with Vaughn, although he's equally enthusiastic about his latest co-star Ayoade, to the extent that he even executive-produced the British director and writer's 2010 film, Submarine.
For Stiller's influence today extends far beyond a mere name above the film title, silently producing numerous movies in which he doesn't even feature, including the comedy Blades of Glory, starring Will Ferrell; horror thriller The Ruins; and the bird-watching dramedy The Big Year, featuring Jack Black, John Cleese and Steve Martin.
So when Stiller sits down to discuss The Watch in a Beverly Hills hotel room, it's little surprise that he views his role in the context of the greater picture. "It's been fun because everybody came in from their own point of view. It's not like you're competing for anything because the script was so well-defined in terms of who these guys are and made very clear sense of what the relationships are supposed to be."
If aliens are a new twist on Stiller's stock-in-trade, R-rated gross-out comedy, then it's little surprise that sex factors largely into The Watch.
Squirming a little as we discuss why penis jokes are so funny, he offers: "I think sex is just something that people can't talk about in public usually. There is suppression of that or a repression that makes anything you can't talk about vaguely forbidden and the humour can come out of that," says Stiller, whose psycho-speak speaks to his own history on the shrink's couch.
"It's all ridiculous anyway, I think. Just to be able to have conversations about stuff like that, especially in a movie like this where maybe this genre usually doesn't have the ability to go into those areas is part of what makes it fun," says Stiller whose character's low sperm count renders him incapable of conceiving a child with his baby-obsessed wife. In real life he's been wed 12 years to his frequent co-star Christine Taylor, together parents to a daughter Ella, 10, and a son, Quinlin, seven.
Portraying the leader of a neighbourhood watch, he is outgoing and disciplined to the point of being compulsive, a trait which he confesses is quite far removed from his own persona. "I'm really not that outgoing or, for that matter, particularly organised," says Stiller who, when we speak, is en route to joining his family at their vacation home in Kauai.
When he returns, he will resume work on his remake of The Secret Life of Walter Mitty, stepping into the role made famous by Danny Kaye in 1947. Co-starring Kristen Wiig, Mitty is Stiller's first outing as director, producer and star since he served as a triple threat in 2008's Oscar-nominated Tropic Thunder, where he co-starred alongside Robert Downey Jr, Steve Coogan and Jack Black.
Mitty has multiple tags of comedy, fantasy, drama and romance. Stiller admits it is an uphill struggle to be taken seriously as a dramatic actor, despite the fact that his first big screen break was in Steven Spielberg's Empire of the Sun in 1987. "I don't think I've done enough serious movies to really tell you what I like better because each experience is its own thing.
"Whether or not it's hard for an audience to see me in a serious drama, is a different question. I just do what I feel is right for me," he says, his poker-faced expression finally adjusting to something akin to a smile. But I'm really excited about this touring version of Of Mice and Men that I'm taking on the road this summer that I'm hoping is going to go really well."
While The Watch was formerly titled Neighbourhood Watch, it was re-titled to distance it from the Trayvon Martin shooting in the US, where a man was slain at the hands of overzealous neighbourhood watch member George Zimmerman. With zero personal experience of neighbourhood watches, he quips: "I grew up in New York in the 1970s. In New York it was more a case of 'Every man for himself'."
'The Watch' opens on 24 August
*This article appears in tomorrow's print edition of The Independent's Radar magazine