Gangster, killer, Aragorn ... Mortensen is not known for his comedy. But in new film Captain Fantastic, his grizzled deadpan is the funniest thing in a very funny film. But get him on to politics and prima donna colleagues, and he is deadly serious

Viggo Mortensen has just been on This Morning. Before his slot on the breakfast show, the actor sat backstage watching hosts Eamonn Holmes and Ruth Langsford present an item about children crying on planes. Feeling playful, he began his interview by saying he liked to scream on planes himself. Kids, he said, asked him to be quiet. There was a dilated moment of live TV silence. Eventually, the uncertain laughter of Holmes filled the studio. “But it’s OK,” Mortensen went on, “because I always wear a helmet when I fly.”

He is still in the slick dark suit he wore for TV. He looks rueful. “It probably wasn’t the right thing to say. The helmet thing.” The presenters, he says, were baffled. “I think people don’t expect me to make jokes.”

At 57, Mortensen is a musician, painter, photographer, writer and owner of an independent publishing house – the Perceval Press – as well as a supporter of esoteric football teams around the globe. “But not much of an actor,” his friend David Cronenberg once wisecracked. Not much of a comedian, perhaps – or, as he says, not known for it. In a 30-year career, his signature movies are probably two he made with Cronenberg a decade ago, A History of Violence and Eastern Promises. In the first he was a small-town dad with a grisly past; in the second, a Russian mobster who stabbed a man in the eye while naked in a London bathhouse. These roles may have played on Holmes’ mind.

But Mortensen’s new film is a comedy, mostly: Captain Fantastic is bittersweet and spiked with radicalism. He plays Ben Cash, raising six children off-grid in the woods of the Pacific north-west. The kids haven’t just been taught to hunt deer and rock climb, but read Chomsky and reject capitalism. In a very funny film, Mortensen’s grizzled deadpan may be the funniest thing of all.

Facebook Twitter Pinterest Viggo Mortensen with George MacKay, Nicholas Hamilton, Annalise Basso and Samantha Isler in Captain Fantastic. Photograph: Everett/REX/Shutterstock

“Really,” he says, “there’s no plan to what I do beyond finding movies people might still like in 10 years.” But fatherhood keeps turning up. Aside from A History of Violence, there was The Road, the adaptation of Cormac McCarthy’s novel of a father and son in a grey post-apocalyptic world. Mortensen has an adult son – Henry, a documentary-maker – from his former marriage to Exene Cervenka, singer in LA punk band X. “Parenting is humbling. You vow to not make the same mistakes your parents made, and then inevitably, there you are.”

Mortensen speaks calmly, on the edge of quiet. “The way the family is portrayed in movies is often binary. You either have the happy family or total dysfunction, where you watch and say: ‘Oh, they were so fucked up, I was so moved.’ The reality is happiness and dysfunction. But that’s less comfortable to sell.”

In the movies you either have the happy family or total dysfunction. The reality is happiness and dysfunction

The politics of his character in Captain Fantastic are not a world from his own. On the first day of filming, he arrived with his canoe and a stack of his own books to fill the family library: Quebecois poetry, Howard Zinn’s A People’s History of American Empire. But nothing is simple. Despite their Marxism, he says Donald Trump would approve of the Cashes for their insularity. The family can become a bubble, a retreat from the world. I tell him this reminds me of the infamous Margaret Thatcher speech about there being no such thing as society, just individuals and families. “Right, I remember Thatcher saying that, using the idea of the family to attack the welfare state. Promoting self-sufficiency to eliminate investment in public projects.”

Mortensen in Eastern Promises, 2007. Photograph: BBC FILMS/Sportsphoto Ltd./Allstar

On movies, Mortensen can tend towards the businesslike. Talking politics, he could go all day. “It was the same credo with Reagan, supported by the media, and from there all roads lead to Trump. Shocked editorials ask: ‘How can this have happened?’ And you think: ‘Because of you.’ But, of course, it’s more complex than Trump. Do you mind?” I realise he wants to get some air at the window. London churns below as he lists the sacred cows of US politics. “Talk about going to church. Say the military is underfunded. Be seen shooting animals. And the Democrats do all these things.”

Mortensen has had an eventful election. An enthused supporter of Bernie Sanders, the selection of Hillary Clinton left him so dispirited he decided to vote for Jill Stein of the Green party. On mentioning this publicly, the response from some fearful of a backdoor Trump victory was raw. The prominent film blogger Sasha Stone wrote a 2,000-word open letter: “Viggo, I expected you to have compassion and regard for the most vulnerable. As evidenced by your recent words, you clearly don’t.”

He half-nods. Clinton, he says, is simply dishonest. “I understand the argument that I’m helping Trump. But people said it was a problem in 2000 voting for Ralph Nader and not Al Gore, and that election was stolen by Bush anyway.” He screws up his face.

Facebook Twitter Pinterest With Maria Bello in A History of Violence, 2005. Photograph: Allstar/NEW LINE CINEMA/Sportsphoto Ltd./Allstar

Nestled in Captain Fantastic is a ticklish idea – that for all his revolutionary theory, Ben Cash is just another patriarch, the oldest white man in the room. To emphasise that point, Mortensen says, there was briefly a plan to have one of the children be adopted from Latin America. “But a film can only tell so many stories.” Still, in 2016, aren’t there times when, if you’re leftwing, white and male, you feel the best thing you can do is just let someone else speak? “Again, I understand that.” He pauses. “The dangerous thing with this conversation is that one thing gets taken out of context, or is underlined. But I’m not afraid of any question.”

Mortensen recalls the premiere of Captain Fantastic at the Sundance festival in January. Standing on the red carpet, he was asked about the news that the Academy was to expand the diversity of its membership before next year’s Oscars. “And I said: ‘Sounds good. But with the Oscars, you should always follow the money. Terrible decisions are made every year because of the money. Because the Oscars are a racket. Yes, there are black performers and Native Americans, and Asians, and Hispanics who are unfairly excluded from this awards circus, but many white performers are too.’ Then the interview appears and all I’m saying is white actors get unfairly left out. And of course there are all these comments on YouTube about how I’m just a privileged Hollywood white guy. And I thought: ‘OK – I should have just said yes.’”

Mortensen’s film career began with a small part opposite Harrison Ford as an Amish farmer in the thriller Witness. He was 27. Before acting, he had worked as a truck driver, shipyard worker and flower seller, pinballing between Europe and the US. The son of a Danish father and American mother, migration defined his childhood too: from Manhattan to Copenhagen and then Argentina, where his father managed poultry farms, until his parents divorced and at 12 he and his mother ended up in Watertown, so far in upstate New York it was almost Canada. (He now lives in Madrid with his partner, the actor Ariadna Gil). Film work proved a slow burn – but Witness hinted at an old world aura others finally saw too. Off camera, he became known for the depth of his research. For Eastern Promises, he had his gangster’s dialogue translated into Russian, then checked its authenticity among people who would know while travelling alone through Moscow and St Petersburg. (More prosaically, Captain Fantastic saw him learn the bagpipes.)

Facebook Twitter Pinterest With his partner, the Spanish actor Ariadna Gil, 2006. Photograph: Alessandra Tarantino/AP

As a parent, research only takes you so far. Before Cervanka had Henry, the couple made plans. “We looked into diapers. Brain development.” He says he learned how a child really defines itself. Still, he rented Henry cartoons on video to avoid commercials, glowed with pride when he wouldn’t join an ovation for Titanic. “And the money I’ve made at times was useful, allowing me to expose him to different cultures.”

Henry’s taste would have a seismic impact on his father’s career. In 1999, Peter Jackson was a day from shooting his Lord of the Rings trilogy when he decided he no longer wanted actor Stuart Townsend in the role of Aragorn. Though Mortensen was offered the job, it had limited appeal; Henry, an avid reader of Tolkien, nagged him into accepting. Three films later, a new level of celebrity had engulfed an actor who had previously answered fan mail by hand.

For somone so self-sufficient, you wonder how strange the film business has been. I mention that the British actor Mark Strong once told me he had to ask an assistant on a blockbuster to stop trying to put his socks on for him. Mortensen winces. Does big budget film-making infantilise?

Aragorn in The Lord Of The Rings: The Two Towers (2002). Photograph: Allstar/New Line Cinema

“It can. But people let themselves be infantilised. And you set the tone as an actor. Young actors see older actors behaving in infantile ways. ‘I want the biggest trailer. I want to go to the premiere in this country and take my family even though the distributor has to pay for the hotel and it’s going to make it harder for them to buy another movie.’ Having their agent fill their contract with privileges then saying, ‘Oh, it’s in my contract’, as if they had nothing to do with it. As adults these are not good excuses.” He stretches out his limbs, his voice fractionally louder. “And the way you behave on set, how you talk to the crew. A lot of experienced actors choose not to even stay around off camera, or do such a poor job on camera it’s obvious they couldn’t give a fuck what you’re doing. I’ve had to say to an actor in a scene where the focus was on me: ‘You know, you seem very tired, why don’t you go home? I’d rather just do this with someone from the crew.’”

“I say this without naming names. But it’s just one example of the piggishness.” He keeps going. He’s on a roll. “Then there’s the sense of competition, fuelled by these mushrooming award shows. Accepting jobs because you might get nominated. Trying to win scenes. They’ve decided to cry because it’s going to get them their nomination, and the other actor doesn’t matter a fuck. But that also happens in independent movies. It’s not unique to studio movies. It’s not unique to American movies. I’ve seen that working in London.

“A movie only works because people adjust to each other. And if they don’t, well, the philosopher Lao Tzu said that if you don’t change direction …” – suddenly a huge grin flashes up on his face and for a second gets wider and wider – “… then you may just end up where you’re headed.”

Captain Fantastic is released in the UK 9 September