ACTOR, writer, musician and photographer Viggo Mortensen had no idea what he was letting himself in for when signed up to replace British actor Stuart Townsend as Aragon in The Lord Of The Rings screen trilogy.

"The shoot was meant to last about a year and we were supposed to have a break and be permitted to go home every third month," he says. "But the shooting lasted 18 months and we had no breaks."

Five years later the Danish-American labelled Hollywood's "true renaissance man" is finally coming to terms with being transformed into an international superstar.

It's been a long time coming. For a decade or more he's been on the brink of screen stardom, with supporting roles in films like A Perfect Murder and Crimson Tide. The delay is attaining starring roles led the 44-year-old Mortensen to once joke: "I've arrived so many times I don't know where I went".

Now he feels lucky enough to have been in the right place at the right time - namely New Zealand, where the Rings trilogy was filmed with him playing Aragon, the exiled heir to the throne of Gondor.

He plays down his contribution by saying: "It's an ensemble piece, it's about the whole group and that's important. There was no big ego that needed tending."

In the final instalment, The Return Of The King, hobbits Frodo and Samwise come to the end of their quest to keep the One Ring from the grasp of Dark Lord Sauron by destroying it in Mount Doom.

Mortensen's Aragorn, who leads the fight against Sauron's forces, is both noble and flawed. "I related to this brave and honourable man plagued by self-doubt and insecurities," says the actor. "Aragon's burden is what shapes and colours his perceptions."

He was so into his role that he spent a lot of time in his fighting outfit "to grow into it" and was even reportedly stopped by a policeman in Wellington while carrying his sword around."

It was his 13-year-old son Henry who encouraged him to leave California for nearly two years of filming in New Zealand. The boy's mother is punk rock singer Exene Cervenka, from whom Mortensen was divorced in 1997.

"There were plenty of reasons not to go, but I would have regretted not doing it so I listened to the voice inside me that agreed with my son, who constantly draws swords and monsters," he says.

SOME can recall seeing actor Andy Serkis in drag in a musical version of Some Like It Hot at West Yorkshire Playhouse in Leeds. But the frock, high heels and make-up he wore are nothing compared to the make-over he donned to play Gollum, the Hobbit gone bad, in The Lord Of The Rings films.

The character, whose possession of the Ring has deformed his body and warped his mind, is a completely digital character. But his voice and movements are all the work of Serkis.

What a pity Academy Award officials denied the actor the right to be nominated for an acting award in the 2003 Oscars, for Gollum is an entirely performance-based digital creation who acts as much as any actor in the film.

Serkis has written a book, Gollum: How We Made Movie Magic, detailing how it was achieved. He recalls how the job was described as providing the voice for an animated character that would probably be about three weeks' work. In June this year he was back in New Zealand to finish post-production, well into the fifth year of his involvement.

The makers decided early on to make Gollum a totally CG (computer-generated) creature because they didn't feel any actor could cope with the extreme physical appearance, nature and demands of the role.

Serkis's job wasn't just to provide the voice. He had to act out the scenes as well, then be replaced by the CG figure later. The actor wore a bodysuit covered in dots to capture his movements, which were replicated in the computer.

Gollum's voice was the result of Serkis's family cat coughing up fur-balls. "The cough becomes a convulsion - making the entire spine ripple in an attempt to eject the mass of furry sick - accompanied by an unearthly wheezing, until finally it comes out. Voila! Fur balls," says the actor.

He witnessed one of his cats, Diz, bringing up fur balls while he was working out how to achieve Gollum's voice. That night, lying in bed, Serkis realised that was the answer - "Maybe he sounds like a cat being sick. Maybe when he says, 'Gollum, Gollum', it's like an involuntary convulsion."

* Gollum: How We Made Movie Magic is published by Harper Collins, £9.99

Published: 11/12/2003