I went ape for Kong

ANDY SERKIS IS SITTING JUST A FEW FEET AWAY from me in a London hotel suite.

An actor who once spent four months working as a futures broker for what amounted to little more than a cameo in Mike Leigh's Career Girls, there's no doubting Serkis's dedication. "I thought it was important - and I pushed my case to Pete - that we remain true to gorilla behaviour," he says. After watching hours of documentary footage and studying the creatures in captivity at London Zoo, he flew to Rwanda to join a research party from the Dian Fossey fund which was studying testosterone levels in male gorillas. Observing a group of 23 mountain gorillas in the Virunga volcanoes, Serkis was often closer to them than he is to me right now, and survived one male gorilla charging in his direction. "You can't watch them from afar," he says. "It was so shocking and so quick. It is bluff display but you do have to act subservient. You have to remain very still and not muck around."

Serkis, who recorded a lot of his own close-up footage of gorillas as a study tool, admits it took a while for people to take him seriously. "When I arrived in Rwanda I met the Minister of Tourism there, and she said, 'What can you possibly get from researching gorillas? King Kong has given such a bad name to gorillas ever since 1933.' And it's true. People didn't know anything about gorillas when the film was made, and it only served to demonise them." The Minister's question was a fair one: what could Serkis gain from doing a David Attenborough? "What I realised from observing gorillas is how idiosyncratic they all are. They're as utterly individual as you or I, because they're so close to us genetically. As an actor, observing them, it was crucial. I couldn't have done it without it." There is a twinkle in his eye. "And they were quite curious about me."

The gorillas are not the only ones. If little is known about the affable and modest Serkis, it's simply because he gives the celebrity circuit a wide berth. He prefers the solitary pursuit of rock-climbing - he once scaled the Matterhorn solo - to the hullabaloo of attending premieres. Married to actress Lorraine Ashbourne, he has two young sons and a daughter and lists his best buy as a Toyota People Carrier. He may own one of only two prop rings used in Lord of the Rings, but unlike Gollum, he is far from being corrupted by power, wealth or fame. As he says, "I think people assume everyone in Lord of the Rings is a millionaire who will never have to work again but that is not the case."

Born in Ruislip, Serkis was chiefly raised by his mother, who taught handicapped children, as his father worked as a doctor in Iraq. Serkis rarely saw him, which may be why he feels a strong devotion to his own family. Despite designs to become a painter, he spent much of his twenties on stage, initially at the Duke's Playhouse theatre in Lancaster, where he studied visual art. "I think I must have been one of the last young rep actors," he notes proudly. In the 1990s Serkis became affiliated with London's Royal Court Theatre, playing the Fool in Max Stafford Clark's version of King Lear and Potts in the original production of Jez Butterworth's Mojo, a role he reprised for the 1997 film.

Also impressing in the 1997 Old Vic production of David Rabe's Hurlyburly, the role of the hyperkinetic Phil rather defined Serkis's early performances: frenetic, fast-paced and aggressive, he was like a wind-up toy with an attitude. "I enjoy high-speed about-turns in thought," he argues, even if many of his characters were all mouth and no mind. But for every Shiner, in which he played Michael Caine's minder, there was a Topsy-Turvy, Mike Leigh's Gilbert and Sullivan tale in which he played their choreographer. By the time of The Two Towers, the second episode of Lord of the Rings, in which Gollum makes his first major appearance, he was toiling away quietly for such established British auteurs as Michael Winterbottom (24-Hour Party People), Julien Temple (Pandemonium) and Gilles MacKinnon (The Escapist).

Yet since Lord of the Rings, Serkis has remained in a luxurious position. He may have played two of the most talked-about screen creatures in Hollywood of late - as well as sporting an instantly recognisable dark quiff, goatee and fierce blue eyes - but Serkis must be the most anonymous star in the business. "For me as an actor, to have the opportunity to play Gollum and Kong - two amazing characters - and yet not to be locked into those roles facially, it's a dream," he says. Jackson has given Serkis an on-screen cameo in King Kong as ship's cook Lumpy, though the actor claims this was not a demand on his part. "I love working in the digital realm. It doesn't make any difference to me whether I'm acting on screen or in the digital realm."

Right now there's no-one better at the latter than Serkis. So confident were Lord of the Rings backers New Line in his performance as Gollum, the company campaigned for Serkis to receive an unprecedented Academy Award nomination for his work. Creating the character physically, emotionally and vocally, he did everything but appear in the flesh on screen. Ultimately, the Academy ruled against Serkis receiving a nod, arguing that a whole team of animators was needed to bring Gollum to life. "They weren't ready to recognise how we are beginning to work with new technology," Serkis shrugs, confessing that he was flattered to be even mentioned in connection with the Oscars.

Ironically, Serkis spends twice as much time on set as his fellow actors playing human roles. Initially filming a scene with his colleagues to give them something real to interact with, Serkis then re-shoots each scene alone, wearing a motion-capture suit. Tiny sensors across his body trace his every move, feeding his performance into a computer to bring Kong to life. The major advance in technology was with facial motion capture, a technique not used on Lord of the Rings. "We were trying things out," he says. "Gollum looked like me, in the sense that the facial structure was built around my facial muscles. But a gorilla's face is completely different. I don't think Pete thought it was going to be possible to pull expressions off what I was doing. But then we saw the facial motion capture tests, and it really worked."

As cutting-edge as this is, there's something very pure about what Serkis is doing; King Kong could just be the ultimate acting exercise, as he apes, well, an ape. He talks about trying to portray "gorilla emotions" that humans will understand. "It is that 'otherness' that I was trying to get at," he says. "Kong is a very isolated, solitary gorilla", a fact that connects him to Ann, the damsel in distress made famous by Faye Wray in the 1933 original and played here by Naomi Watts. As before, Ann is used as bait to placate Kong and lure him from his home of Skull Island back to New York. "Their relationship is based around unconditional love," says Serkis. "People do have that kind of love for their pets - people are very strongly devoted to their dog or cat. The sexuality isn't that much of a deal in King Kong. It's more to do with a real truth and honest openness of heart that they experience."

Judging by early behind-the-scenes footage of Serkis's uncanny simian behaviour, it seems the only thing he hasn't done is climb up the Empire State building. He praises Jackson for creating the overgrown world of Kong's habitat "given that now GPS covers every square centimetre of the planet", but Serkis's performance appears to be equally exotic.

He's back down to earth as a knife-throwing villain in the forthcoming British teen-spy film, Stormbreaker, but he would like to follow Jackson into film-making. There are two projects he's looking to direct - an adaptation of Stephen Smith's autobiography, Addict, and the story of the photographic pioneer, Eadweard Muybridge.

With Jackson as a mentor, that would be something he could beat his chest about.

• King Kong is released on 15 December.