The question is simple, but the answer is complicated. Asked how playing Aragorn has affected him, Viggo Mortensen struggles to reply, trying to put the experience - three films shot at once, released over the course of three years, with several weeks of additional photography squeezed in before each release - in perspective before actually tackling the query itself. 'After four years on a job like this you get to know the character fairly well,' Mortensen says. 'I invest as much of myself as I can when I'm working on it, and I take pride in doing as good a job as I can. That means bringing any influences I can into what's there, beyond what's in the script and beyond what happens on the day on the set.

'I find it interesting, that process of researching,' he continues.

'Even now, when we went back to New Zealand this past summer after almost four years, there were new ideas that I had or new things that I found in the book or other places. I'm sure that's true for the other actors, too. You change as a person. A lot of them were quite young and relatively inexperienced when they started, and the way they approached the work this past summer had a different, more mature focus. That's natural.'

As The Return of the King closes out the Rings saga, Aragorn rallies the troops for the final battle, as he buys time for Frodo and Sam to reach Mount Doom. 'This is a war mythology, as opposed to a peace mythology,' Mortensen explains. 'It's basically "an eye for an eye' when someone attacks you, not "turn the other cheek'. But like most things, like the nature of Evil, or the contradiction between free will and fate, those things are mixed in the story. Even for Aragorn, who is in some ways one of the ultimate warriors in the story, there are moments when he turns the other cheek, like say with Wormtongue. Whereas a character like Boromir or, in a more lighthearted way, Gimli, is someone who just likes to get in there and get in a fight. Aragorn does not go into any fight lightly. That's the responsibility he has in the story. I don't have a problem with that. I'm not a fan of war, and I don't think that Aragorn is, either. But these are skills that he's mastered in his time and these are things that he has to do.'

The central lessons of The Lord of the Rings play out again in Return. It's the little guys, literally and figuratively, who are among the saga's greatest heroes. Victory and survival must come at a great price. It takes desire and sacrifice and teamwork to ward off defeat. 'Frodo and his Hobbit friends are essentially the ones that get this thing done, with our support,' Mortensen points out. 'Many characters sacrifice themselves. Gandalf gave himself over, he bought them time by fighting the Balrog in Moria. Sam literally carries Frodo on his back in the third movie. Aragorn repeatedly puts himself in harm's way, as do Gimli and Legolas. Going to the Paths of the Dead is something that is vital, but it's also personally a big risk for Aragorn.

'Also, for 70 years, Aragorn has quietly worked to protect the Shire and fought to protect Rohan in years past. Now he has to be a public figure. He has to admit who he is and stand there - he has to run for office, in a sense. He has to not only take risks himself, but he has to convince Legolas, Gimli, Merry, Pippin, Eomer, Gandalf and all the armies of men to go to the Black Gates on what is without a doubt a suicide mission. He has to use the strength of his character and whatever other tools he has to convince all of these people to march towards their death in order to buy Frodo and Sam a little more time on their desperate crawl to Mordor. That's like Gandalf standing against the Balrog; it's futile, but now you're involving so many more people.'

The sacrifices that the battle against Evil involve are clearly on Mortensen's mind, so it's no surprise that he has strong views about the current situation in real life. Indeed, he was widely criticized for having likened President George W Bush to Sauron and Bush ally John Poindexter to Wormtongue during interviews to publicize The Two Towers. But as with those who complain about changes Peter Jackson's made to Tolkien's original text, the actor simply chalks up any negativity to experience and accepts that there's no pleasing everyone.

'I don't make a practice of going on the computer and looking and seeing what's going on,' he says. 'I know that things are there. Every once in a while somebody will make an attack on something I said, or thought I said. Sometimes I think that has more to do with that person's life and is something about them, and I don't try to get involved in that, and I try not to take things too personally.

'Interviews are a part of my job, but I did my job in New Zealand. I'm proud of what we've done. I'm proud of the friendships I have. I'm proud to have worked with someone like Peter Jackson. Of all the qualities he has, his focus, his vision, his stamina just to get the job done, to me, in how I've seen him behave with everyone else, he's essentially a decent person. So all those things I feel good about. The results of how people react, that's just a strange thing that I don't see connected and I'm not going to spend too much time worrying about it.'

But people do react to him. Mortensen was a working actor before the trilogy began, with credits including The Texas Chainsaw Massacre 3, the Psycho remake, Crimson Tide, Portrait of a Lady, G.I. Jane and A Walk on the Moon, but The Lord of the Rings has put him on the map. Nowadays the actor - a private and quiet guy - is in the spotlight, and it's been a mixed blessing.

On the one hand, he's getting a shot at leading man roles - case in point the upcoming biopic Hidalgo - and people are more interested in his photography, poetry and paintings. On the other hand, he's suddenly public property. 'If I'm walking with someone I will know first if somebody else is coming in my direction to ask for an autograph,' he notes. 'I will know before anyone else I'm with because I'm almost unconsciously watchful for it. That's normal. I think you get used to that. If you're just standing there at an airport and someone is staring at you, you don't think, `That person is psychotic. What are they looking at?' You realize that they're recognizing you. I'll say hello. Sometimes, if you're in a hurry or if you're in a public place and you're having a personal discussion with somebody or you're having a difficult day, then it's a little odd to be watched. But I don't feel I'm always watched. I'm able to make my own way around town. It hasn't felt oppressive and I'm flattered that, not just on my behalf, but also on behalf of the storytelling team, that these films have had an effect on people. I'm glad that it's had an effect on people.'

MORTENSEN'S MOST MEMORABLE MOMENT

He just can't do it. There's simply no way Mortensen can choose a single favourite moment from the Rings films or recall a day that proved the most emotional of all. 'I can't pick one,' he explains politely. 'I've heard people say the third movie is their favourite, but to me it all runs together as one long piece, just like all of the days. Every day had some sort of emotion going on.

'I know that people are talking about the third movie in that way or saying that certain scenes were more intense than others. I know that the third movie combines a lot of the elements from one and two. It's got the more subtle, intimate inter-relationships and emotional, personal stuff of the first movie and it's got the scope of the second movie. It takes both of those elements to new heights. Story-wise, it's complex. There are so many elements that have been winding their way in different directions, more or less parallel, and now they have to be brought together into one strand. They have to become one story by the end of it. That was a challenge for Tolkien, and it's been a challenge for Peter, one that I think he's really pulled off.'

ONE RING TO RULE US ALL?

Rings fans revel in debating the true meaning of the One Ring. Some see it as the source of all Evil. Others view it as the tool of Middle-earth's redemption. Some see it as a symbol of fate that the Ring can, will and must be used to defeat Sauron. Others consider it a symbol of free will in that the Fellowship chooses to rally around Frodo in a joint effort to destroy the Ring. Mortensen has spent plenty of time reading Tolkien, and studying religions and philosophies, and he's formed an educated opinion on the subject.

'The Ring itself represents the potential for any one of us to not put the group first and the temptation to get ahead by trying to control other people's wills,' he says. 'If there's anything that's close to Evil - and I don't think there's absolute Evil in the world or in this story; it's more complicated than that - it doesn't reside in the Ring or in Mordor or in Sauron himself. It's anywhere. It's in moments where characters are tempted to not take care of their fellows, to not do the right thing. It's clear, at least to me, that doing the right thing is its own reward.'