Philip Seymour Hoffman interview: Whirlwind of weird

Whether wrangling with whirlwinds or tormenting cerebral critics, you can always rely on Hoffman to be the offbeat, provocative note in any film. Now he's teamed up with another of cinema's leading brainteasers, Charlie Kaufman, for Synecdoche, New York. The result is typically weird.

The film marks Kaufman's move from writer to full-on auteur, after penning such philosophical paradoxes as Being John Malkovich and Adaptation. Hoffman plays a frustrated theatre director who embarks on his biggest production to date, set on a stage that is a life-sized replica of New York City. During rehearsals that go on for more than 17 years, he hires a huge cast of actors to play himself and all the people in his life. In any ordinary actor's CV, this would be enough to put Synecdoche in the oddball Top 10 but Hoffman has spent more than a decade carving himself one of acting's most admired – and strangest – niches.

A transsexual in Flawless, Lester Bangs in Almost Famous, an obscene phone-caller in Happiness, a secular, music-loving priest whose fingernails are a little too long and whose attitude is a little too lax for Meryl Streep's nun in Doubt: these are all portraits that hang on Hoffman's wall, yet Synecdoche provides a special challenge beyond physical and vocal dress-up.

Hoffman was drawn to it after reading "one of the best scripts I've ever read", and he describes Kaufman as "terrific, so bright and one of the most deep feeling and thinking people you'll ever meet. "It was hard material, incredibly complex," he continues. "I'm trying not to be overly effusive but I can't say enough. I adore him and I'm so glad he asked me to do it. That was one of those things, where you just say, thank God he asked me!"

What always makes his antenna twitch is a character with a pet fixation. In Synecdoche, New York, his director starts tracking his own life because he is disturbed and obsessed by his own body's physical deterioration.

"Somewhere in your mid to late 30s, going into your 40s, the idea that you're not young any more and things are changing starts to overcome you," says Hoffman, who is 41 and has three young children with his partner of a decade, the costume designer Mimi O'Donnell. "When you have kids and all those things, health becomes more of a question than it ever did before. You are aware of the maintenance of your life, whereas before you weren't so aware of that."

Raised by his mother, a civil rights activist, Hoffman took up acting at school in order to impress the girls, like so many before him. He studied theatre at New York University and continues to do stage work when he isn't filming; his acclaimed LAByrinth production of Stephen Adley Guirgis's Jesus Hopped the "A" Train transferred to the Edinburgh Festival then London's West End in 2002. More recently, he directed the West End play, Riflemind, last autumn with John Hannah as the leader of a reformed rock band. It closed early, however. "We weren't getting enough of an audience at a certain point. The reviews were pretty tough, but it happens, that's the business I'm in."

We've come to expect at least one Hoffman film performance per year, but he raised the bar recently with three in three months. Before Synecdoche, he was the freethinking priest in Doubt, and came aboard The Boat That Rocked as the only DJ on Richard Curtis's pirate ship that you could see yourself tuning in to. While the other actors were put through what Curtis called "Boat Camp" to acclimatise to their roles as platter spinner, Curtis says Hoffman arrived for filming with his character already worked out, a rasping abrasive called The Count.

"I really like him a lot actually," says Hoffman of Curtis, and that's possibly because if there was a diffident interviewee contest, Curtis would be his closest competitor. "I really can just sit and talk with him for hours. There was a lot of stuff filming on a boat, in the middle of the ocean, off Weymouth. It was a great group."

One of Synecdoche's best jokes is that the alter-ego hired to portray Hoffman in the stage production is leaner and taller. Hoffman is stocky and strawberry blond, and more handsome than many of his characters, but directors and cameramen love to shoot him in ways that make him look weaker, and thicker. Thicker isn't always an optical trick. On the aforementioned Twister, Hoffman looked a stone heavier or lighter from scene to scene due to his excitement at discovering that the blockbuster budget extended to the on-set catering, which was free and plentiful. When he was cast as an obnoxious prep-schooler in Scent Of A Woman a couple of years earlier, he was still supplementing his income by serving in a deli.

The days of sneaking free food ended with Boogie Nights, and was consolidated by his Oscar win for Capote, in which he channelled the diminutive self-promoting writer and raconteur with such authority that it's hard to believe Hoffman doubted his ability to play him in the first place. He's now famous enough to draw ghostly stares from passers-by, fellow diners and hotel waiters – lingering looks that are lit by a vague recognition. It's a state of quasi-fame that rather suits his purposes. In conversation, Hoffman protects his privacy by adopting a defensive fogginess, but that abruptly clears when he warms to an idea that interests him. On his way to France for the world premiere of Synecdoche, he says, he was reading a book by Hollywood screenwriter William Goldman.

"He's a wonderful writer but there's a point where he says that when actors become actors they know what they're getting into." Hoffman disagrees: "I'm sure there's a group of actors that want to be in the movies, and want to be movie stars. But there's a whole bunch of us that got into acting because we went to our regional theatres and saw All My Sons. Or wanted to do Off Broadway and ride a bike to the theatre. That's what I thought was going to be my life. I had no idea I was going to be on a screen."

• Synecdoche, New York is released May 15