David Harbour was an unknown before taking the part of the grizzled and grieving police chief, Jim Hopper, in Stranger Things. He was a minor act in major films such as Brokeback Mountain and Quantum Of Solace, but Hopper made him famous, fast.

He admired the complexity of the supernatural Netflix show’s pilot, but there was something else about it that appealed too. In his twenties the actor was diagnosed with bipolar disorder, was sent to hospital and continues to take medication to this day. And in the character played by the show’s breakout star Millie Bobby Brown, Eleven, he saw a “superhero” with an undercurrent of mental illness. In his character, meanwhile, he saw a man battling depression over the death of his daughter.

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“It’s a show that you can watch with your mentally ill ten-year-old,” he says, sweetly, “and feel some degree of peace and happiness when you watch Eleven and Hopper struggle through their world.”

I’m speaking to Harbour in his native New York. His voice is deep and gravelly and the conversation is fun and unpredictable. He says things such as, “We’re all on this human journey and we’re all going to die” – but it’s never miserable.

Harbour didn’t talk publicly about his mental illness until he was famous. He was worried the stigma of being unreliable would have cost him work. “As an actor,” he says, “you’re worried about getting hired, but now I’m at a place where I can talk about this. Also, I’m in my forties” – Harbour is 43 – “I may as well be myself, whether I get work or not...” He stops and laughs a little before continuing.

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“My biggest reason for getting into it, though, was I imagined a mother of a kid who is taken out of school, diagnosed childhood bipolar. The mother feels it’s a death sentence, that their kid will never be part of society, [that] they’ll always be on the couch eating pizza and, at times in my life, I was that guy. So I want to say if you admire this profession, which you don’t have to, then I’m no different to that child. That’s what I want to share with those people, because they suffer like my parents suffered.”

To simplify, I say, you want to say their child will be OK. “Yes, to simplify,” replies Harbour, cautiously. “Or, if not OK, I’m at least contributing. I struggle on a daily basis. You try to normalise it, but non-normality is interesting too. Embrace your neuro-atypicality! Making it as if you’re the same as everybody else is a lie and it sticks in the craw of the mentally ill. Mental illness is a disease that’s wildly misunderstood.”

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About Stranger Things, set for a third series in July, he says that he knows where the story is going for Hopper and that it’s “very beautiful”.

“Hopper is, above all, a man of justice and he will end up a man of justice. It’s satisfying, but not saccharine,” he says.

All of which, frankly, makes it sound like he dies – but that’s drama Harbour would admire. The actor had classical training, dropping the names of Achilles, Hector, Henry V, Coriolanus, Hamlet and Titus Andronicus into our chat. “You don’t hire me because you want The Rock,” he explains. “I’m more of a psychological actor.”

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Before the return of Stranger Things, though, he is in a big-budget film, Hellboy, a reboot of the 2004 Guillermo del Toro graphic novel adaptation. It’s a big deal for Harbour, given it’s his first as leading man, or monster. The story – the “Blood Queen” (Milla Jovovich) is roaming around England wanting to bring about the end of the world – is more violent than previous Hellboy films. But Harbour insists there is philosophy throughout: a constant questioning of whether the planet, as it is now, is worth saving. Maybe, a suggestion is made, hell is better.

So he likes intense subjects, but that has been obvious since he appeared at the Screen Actors Guild Awards in 2017, accepting a prize for Stranger Things. In a speech also memorable for Winona Ryder’s erratic facial expressions, Harbour went off about how the show was there to “shelter freaks and outcasts”.

It sounded more political than it was. Instead, it was about his profession and how his peers are too flawless these days. “The trend is for us to work out,” he says with venom. “Then stand up on screen and dazzle the world with godlike perfection. But I got into acting because of Walter Matthau. I like the dudes who are less-than-capable seeming, who then overcome odds. That’s much more dramatic, but we have to battle narcissism on every level – this navel-gazing self-love. As artists, the primary purpose is to reach out to the discomfited and to say to the comforted that, maybe, you should feel a little more discomfort. But it’s becoming harder to do that.”

Hellboy is out on 11 April. Stranger Things series three is on Netflix from 4 July. Styling: Michael Fisher. Grooming: Charlie Taylor. Tailor: Jenny Barone at 7th Bone Tailoring. Photography assistant: Jon Vachon. Styling assistants: Hannah Neser; Amber Simiriglia

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