The 6ft 4in Swede on taking on Tarzan, football and how he got an eight-pack.

Mr Alexander Skarsgård stands on the rooftop of a Manhattan skyscraper, looks out onto the urban jungle below and thumps his chest. For a moment, it looks like the man who plays Tarzan might be about to let out the mythical character’s signature call of the wild. Turns out he’s just trying to clear a chesty cough. “Sorry, bad cold,” he croaks. The day before this interview, Mr Skarsgård had flown to LA and back within 24 hours – hence picking up the man-flu.

From up here, the 6ft 4in, 39-year-old Swede can just about see where he lives in Manhattan. After today’s shoot, he is due to accompany his girlfriend Ms Alexa Chung, the British model and It girl, to the CFDA Awards, a gala night on New York’s fashion calendar. In the morning, he’s off to Tokyo for a Tarzan premiere and then, if he can swing it, he’ll fly to France to see Sweden’s football team play in the European Championships.

Such is the life of a leading man. In The Legend of Tarzan, Mr Skarsgård heads up an all-star cast, with Ms Margot Robbie as an anything-but-plain Jane, Mr Samuel L Jackson as Tarzan’s unlikely sidekick and Mr Christoph Waltz doing a wonderful turn as the villain of the piece. The story begins with Mr Skarsgård playing John Clayton, Third Viscount Greystoke, living a humdrum aristocratic life in England with his wife Jane. Things take a decidedly less-genteel turn when they’re called back to the jungles of Africa, where he was raised by gorillas as a feral child called Tarzan.

Mr Skarsgård’s own childhood was wild in a rather different way. He was brought up on the island of Södermalm, a free-thinking community of artists and writers in southern Stockholm, the eldest of six children – five boys and one girl. “It was an incredible childhood, it really was. No one ever locked the doors. We didn’t even have keys,” he recalls. “My cousins were in the apartment above us, so the kids would just run up and down. And Grandma and Grandpa lived across the street.”

Mr Alexander Skarsgård’s father, Mr Stellan Skarsgård, 65, is Sweden’s most famous and best-loved actor who has appeared in Thor, Good Will Hunting, Mamma Mia! and The Girl With The Dragon Tattoo among many others. The legend of Stellan is an entertaining one. By all accounts, his liberal approach to life extended to his wardrobe. He often walked around the house naked despite the presence of guests, which may or may not explain his eldest son’s relaxed attitude towards nudity. (Mr Alexander Skarsgård famously went full frontal in the season six finale of True Blood.)

“My dad is a very social guy. He loves to cook. We always ate together as a family every night,” says Mr Skarsgård. Even after his parents divorced and his father married someone much younger with whom he has two more sons (that’s seven sons and one daughter – are you keeping up?), they remained best friends. So much so that they still dine together as a large and loud extended family most evenings and even bought holiday homes 200 yards away from each other. “It’s very unusual. I’m very aware of that and how lucky we are,” says Mr Skarsgård. “Almost all my siblings live within a four-block radius and every night my dad will cook for whoever swings by. There’s a big dinner party almost every night of the week.”

As a child, young Mr Alexander Skarsgård did some bit-part acting here and there before, at 13, landing a lead role in Swedish TV production Hunden Som Log (The Dog That Smiled), which made him abruptly famous. Uncomfortable with the recognition and the attention, he decided he didn’t want to act anymore – a decision his father supported. “Dad basically said: ‘Well, if you’re not feeling it, don’t do it. Go do other things, have fun, enjoy your life’,” says Mr Skarsgård. “I’m very grateful for that because if he had pushed me, I don’t think I’d be an actor today. I needed a break from it in my teenage years.”

Mr Skarsgård spent those teenage years doing typical teenage things like getting drunk, listening to punk and following his beloved football team Hammarby home and away. Then, at the age of 19, he surprised everyone by announcing he wanted to do his national service.

“I grew up in a very Bohemian hippy-dippy environment,” he says. His entire family are artists and pacifists – wine-drinking, pot-smoking people who hate the idea of the military. “Maybe, age 19, [signing up] was a reaction to that.” Not that he had any intention of seeing active service. “I wasn’t going to get sent to a war zone. In Sweden, our last war was 200 years ago, so it was more of a personal challenge. Obviously if you enlist here in the States, it’s a different conversation.”

Mr Skarsgård isn’t afraid to get out of his comfort zone. After 15 months with the Swedish marines, his next immersive educational experience was to study in England – and at random he picked Leeds, “a tough working-class town”. Why Leeds? “Well, my buddy and I wanted the full British experience. We thought, ‘If we go to London, we’ll just hang out with all our Swedish friends there’. So we looked at a map and I saw Leeds. I didn’t know anything about the city at all apart from Leeds United.” He still supports the team, despite their demise in recent years from the heady Champions League days in 2000-2001.

Eventually, perhaps inevitably, Mr Skarsgård returned to acting. Despite their father not putting any pressure on his children to follow his lead, Messrs Gustaf, Bill and Valter Skarsgård have become actors alongside their brother; it’s clearly in the genes.

Mr Skarsgård’s breakout role was a memorable cameo as a ditzy male model in Zoolander (“Earth to Meekus”). But it was his military training that helped get him his big break as the lead in Generation Kill, an HBO mini-series about the Iraq war. And straight after that, he landed his best known part, that of Eric Northman, a 1,000-year-old bar owner in HBO’s cult vampire series True Blood, which ran for seven hugely successful series from 2008 to 2014.

Although Mr Skarsgård has deliberately tried to avoid being typecast, there is a common theme to most of his roles: he normally has to get his kit off. So, with one full-frontal under his belt, he’s pretty comfortable without any clothes on, then? “Yes,” he concedes. “Although obviously you don’t want it to feel gratuitous.”

In The Legend of Tarzan, Mr Skarsgård spends most of the film running and swinging and grappling without his shirt on. Warner Bros offered to pair him with one of their trainers to get him in shape, but he asked to work instead with his friend Mr Magnus Lygdbäck, a trainer-nutritionist and fellow Swede whom he’d got to know socially while living in LA. “When you have to see the same person every morning at 4.30am, it’s important you get on well with them,” says Mr Skarsgård. Naturally lean of frame, he spent three months bulking up, adding 25lb (more than 11kg) by eating “an insane” 7,000 calories a day (three times his usual intake) and lifting heavy weights. Once he got to the green screens of Warner Bros’ Studios in Leavesden, just outside London, for eight weeks of preparation followed by four months of filming, he embarked on a very strict sugar-, gluten-, wheat-, dairy- and alcohol-free diet of six smaller meals per day alongside his twice-daily training sessions in order to chisel his eight-pack.

Although he hates dieting, Mr Skarsgård loves an intense physical challenge. In 2014, he trekked to South Pole with Prince Harry to raise money for charity. “He’s an incredible storyteller, so I think he’d be a very good actor,” says Mr Skarsgård of the prince. He also spent three weeks at sea a couple of years back, sailing across the Atlantic. So is he more at home in the wild than in the urban jungle? “I’m definitely a city guy, but I love the contrast, to get away for a complete break, with no phone,” he says. “That recharges my batteries.”

Depending on the success of this Tarzan reboot, he may have to get back into the roped-vine swing of things again soon. He has signed a three-movie deal and it doesn’t give too much away to say that everything is set up for a sequel, with Tarzan and Jane living back in the jungle with a new loincloth-diaper-clad arrival.

Having grown up in such a large and close family himself, is Mr Skarsgård planning one of his own? “Yeah. I’m not married, I don’t have kids,” he says, a little ruefully, and then tails off. He turns 40 in August, and would be forgiven some introspection at the imminence of such a landmark. “I feel OK about it,” he shrugs. “No midlife crisis yet.”

The Legend of Tarzan is released on 1 July in the US and 6 July in the UK