If the Academy Awards had a "Best Chameleon" category it would surely have been owned by Renée Zellweger these last few years. This decade alone, Zellweger, 38, won over legions of Bridget Jones-lovers adamant that their "Bridge" really shouldn't be played by a Texan (and you had to see their point). She deservedly earned her first Academy Award nomination for the role, her second the next year for Chicago, before winning as Best Supporting Actress for Anthony Minghella's Cold Mountain in 2004. She gambled on Down With Love with Ewan McGregor, gained the hated weight once more for Bridget Jones: Edge of Reason, starred with Russell Crowe in Cinderella Man and McGregor again for Miss Potter. Jerry Seinfeld, then semi-retired but still powerful, hired her to voice his "queen bee" in Bee Movie, only Zellweger's second animated movie and finally, last year, she found time to work with her "dear friend" (they use the same term for each other) George Clooney.
Set against a backdrop of American Football in the mid-Twenties, Leatherheads had been gestating in Clooney's cluttered head for about a decade. He says he wrote the role of pugnacious Chicago newspaper reporter Lexie Littleton with Zellweger in mind.
"She was the only person I ever thought of to do it. Three or four scenes were written in the original script that really sounded like her voice, and then you just had to think about Renée delivering them. She is so good at this kind of stuff. There are very few actors, not just actresses, but actors that don't feel contemporary. If you took them and put them in a period piece it feels like it's 2008 in the middle of a period piece. And she doesn't. She's really good at being able to do that."
Littleton indeed channels a mood straight out of Hepburn-Tracy country. Zellweger is quick too in person but very different from Littleton. "I love that she's so sexy and confident and brave."
Tellingly she adds, "I don't feel safe playing the girl who looks like me," and breaks her near-constant eye-contact for a moment to fiddle with her rather shapeless long-sleeved black T-shirt. "There's not enough to hide behind. The further removed the character's reality is from my own, the more fun and easier it is."
She says she likes tools to work with – costumes, accents – but is not a woman to adorn herself. Today she wears what has become a sort of uniform – that dark T-shirt, jeans and invariably trainers. She has at times drawn media attention for her weight, or lack of it. "I'm a constant 110 pounds," she protests, "I don't like sweets but give me pasta in Rome and I'm like nobody's business."
Her fleeting 2005 wedding to country star Kenny Chesney that saw her gracing the sort of tabloid pages she would rather not; first a beaming photo from the idyllic-looking day and then the account of her filing for divorce on grounds of "fraud". Otherwise, Zellweger rarely features in any form of tabloid media unless she is grabbing a coffee at Starbucks en route to a set.
"I like a good day at work," she says, "and it's not really an addiction. I'm learning things and I like to be busy and I have a curious mind and I like to be occupied with something that feels worthwhile to me. I like a challenge. If the moment isn't filled with something chances are I'll find something."
She and Clooney speak weekly, text constantly and, Zellweger says, "see each other all the time". They have been dogged by rumours for years. Zellweger wears them well, as any sensible girl should.
"I'm fine with it because what they do write is so much more interesting and makes me so much more an interesting person, especially when they say George Clooney is my secret husband. I'm a terrible terrible movie star. I'm not good at it. I'm really not. I can pretend to be but it takes a lot out of me. It's not my natural inclination to go, 'Goody! Talk show!'"
She turns 39 this month, so is well used to questions about the possibility of her becoming a mother. "I don't think about that. I'm not single, I'm busy. I will worry about that when the day comes. I just want to do my best to be a good friend and a good daughter and a good sister and a good aunt [to her brother Drew's children]."
Born in Texas to Swiss- and Norwegian-born parents, Zellweger excelled at school, academically and in sport, and planned on becoming a journalist before acting derailed that plan. Nothing about Zellweger is typical, not least her refusal to jump on a bus for Hollywood. Instead, she stayed in Texas winning roles in locally shot films like Richard Linklater's Dazed and Confused (which also launched Ben Affleck and Matthew McConaughey) and 8 Seconds, starring then-Beverly Hills 90210 star Luke Perry.
"I have no regrets about that, none," she says of moving away from Los Angeles. She says she hasn't lived there properly in a while, despite plunking down nearly $7m for the requisite Bel Air mansion more than five years ago. Now she owns an Upper East Side apartment in Manhattan, which she calls home, seemingly reluctantly. "What's home? Where my bed is and stuff,"she says.
Though she also owns a home in the Hamptons, one in Connecticut and a 39-acre plot in Tennessee, Zellweger has been eulogising the virtues of living out of a suitcase for some time now. She says that, after years of sleepless nights in hotels, she is finally able to sleep wherever she lays her head. "It's just a hotel after a while, isn't it?" she says breezily, as if we all live her peripatetic life. "I know. It's terrible to not be impressed by being spoilt rotten, but spoilt rotten is sleeping on my best friend's couch because I love private moments with people that are real."
When not working, she says, she's an avid surfer, and registers my surprise. "I prefer to call it surf-ish. I surf-ish. I don't have a lot of time to get good at anything because usually I'm contractually obligated not to surf or do anything fun. No motorcycles, no water-skiing."
Surfing provides precious alone-time. "That's just how I'm made. I ride my bike, I run, I read, I play my piano and guitar and write really bad songs; short stories and poems that no one will ever need to see. So this job's a really good idea, right? Nice choice, lady!"
'Leatherheads' opens in the UK on 11 April