Focussing on the 1980s, when Maradona resurrected Italian team SSC Napoli and later won the World Cup with Argentina, it's a film that tests whether a viewer can hold their breath for 120 minutes as Kapadia lands a windfall of previously unseen footage to tell, arguably, the ultimate story of triumph and despair, on and off the pitch. There are no talking heads on screen and not a word wasted.
Below, the director tells Harry Guerin about why Maradona agreed to take part in such a soul-searching study of his own flawed genius, which sees him "saying things he's never said before".
My knowledge of Diego Maradona within football was every four years when there was a World Cup.
I didn't know what happened in between the World Cups; I didn't really know what happened off the pitch. I remember latter Maradona, when he was in a bad way. I remember being really shocked when I first saw him looking quite obese. So my question is always: 'What happened? How did that happen?' When you come out [of the film] you think you knew the story, but actually you realise there was so much you didn't know.
The fear of the unknown makes him quite intimidating.
You hear these stories; you don't know which version of Diego Maradona you're going to meet. Is he going to hit me if I ask him a question he doesn't like? But of course the issue is it takes ages to get to meet him, and then once you meet him he's a nice guy.
I went to his home; he's sat on his sofa watching Boca Juniors on TV while I'm trying to interview him.
He's really charming and he has a great smile and he's quite sweet. So if you see him at the right time and you're talking about the right things, he's really charismatic. He's a great storyteller; he's got a good sense of humour and a great memory.
But on a bad day you're listening to him and you're thinking, 'I don't think any of this is usable'.
I'm not quite sure what he's saying, even if he's constructing sentences. Is that because he's tired? Is that because he had a bad night? Is that because he's not well? I don't know. So there were times, which is a new thing for me when making these films, where I almost cancelled the interviews and said, 'Let's just do this another day because you're not sounding great'. But that might be 24 hours after he sounded perfect. So it all depends on the day of the week sometimes. You don't know what's going on when you walk away.
The deal on this film was, contractually, I had three interviews with him, each of three hours. For me, that's not a long time.
It would take weeks or months to get to meet him. On Senna I did many interviews with people, but they were five hours long. If I'm lucky I might use some of the last 15 minutes and then I'll say, 'Can I talk to you again? We've only just started, really'.
With Maradona I kept trying to get a little bit deeper.
I'd mention a person and he'd say, 'Don't mention her! I don't want to hear about her! Never bring her name up!' And you go, 'Right, ok. That's one of my easy questions!' And I'd go, 'What about this guy?' 'Never bring him up again! He stole from me!' You think, 'Ok, that doesn't leave much!'
So we talked about his family, his parents.
That always puts him in a good sentimental place, I suppose, his upbringing. And then we stuck to football for a while and I got a few 'bankers' in. I said, 'Ok, we've done the middle. We've got the heart of it. I've got some difficult questions, I'll save them up for the next trip. But I'll do a bit more homework and research'. We edit for another year and go back and talk to him again.
It was really my penultimate interview where I felt, 'Ok, I have to deal with these subjects, to him, because they're in the film'.
Those subjects were his relationships with women, his relationships with his children that he didn't recognise, drugs and addiction and his friendships with the underworld in Naples.
But Diego Maradona is a pro when it comes to answering any difficult questions.
I will ask him a tough question and he will give me a brilliant answer - about Sepp Blatter or FIFA or something entirely different. There were some great lines in there, but you're thinking, 'That's not really useful to me'. He knows most journalists will go away and they've got their quote and everyone's happy.
So I'd have to interrupt him, which isn't the done thing.
He did get quite annoyed. That's when I saw someone looking at me quite seriously and saying, 'I've got to tell you, you've got a real nerve asking me those questions. You've got a nerve saying this to my face. But for that, I respect you'.
I don't know if he genuinely trusted me more than the other filmmakers who knocked on his door.
But I do know that he liked Senna - he'd seen the film and liked it and he was a big fan of the man. That helped us. It helped that while my producers were trying to do the deal for the archive and trying to do deals for Diego Maradona's licensing rights and his image rights with his lawyer Amy was on an awards run and won an Oscar around the time while we were trying to finalise the deal.
It also helped that I work in a slightly different way.
I'm not trying to hang out with him. I don't want to be his mate. I just want to ask him the questions. I also know that even if he didn't co-operate I could go off and make the film like I made Senna and Amy. I wasn't able to meet them, I didn't interview them, but we made the films. So there's a way of making these films without the 'lead character'. I thought, 'I'd like to have him on board'. And he was on board.
I backed everything up by talking to everyone else in his life.
I spoke to his ex-wife. I spoke to his children. His trainer, Fernando Signorini, is a very key figure who I'd never heard of before. He probably knows Diego Maradona better than anyone, mentally and physically. His biographer, Daniel Arcucci - who spent 30 years following Diego around - he's part of the film. A lot of the people may not be well known to us here in Ireland or in the UK, but actually they're key parts of Diego Maradona's life for a long period of time. They're the people I showed the film to in the end.
They saw the film and said: 'It's tough. It's honest. He's saying things he's never said before, but definitely you've nailed it'.
I'm quite sympathetic to him because having made a film already, Amy, I'm not going to judge everyone by what's been posted on social media, what people are saying. There's the idea that everything's about money - 'These guys, all they care about is money' - but actually, with Diego Maradona it's about respect and someone treating him a certain way. And actually just giving him the time. There are times when he doesn't feel in the mood for doing press or doing an interview, and you have to respect that. I think that's what was interesting.
He still hasn't seen the film.
I've tried to show it to him. I was ready to go back to Dubai, where he was living, where I interviewed him. Just as we were about to go to Dubai and I thought, 'We've got a movie now. We're nearly there', his people said, 'No, no, he's going to Belarus. He's got a new job in Belarus. He's coaching'.
So we're going to go to Belarus and then I get told, 'No, he's going to Colombia'.
I say, 'Ok, I don't think I'm going to get to Colombia. What's he going to do after Colombia?' They told me, 'He'll be at the World Cup. Come to Moscow'. I just thought, 'The World Cup, Moscow - this is not the time to show him this particular movie'. It's quite heavy at times.
Then he says, 'I'm going to be in Argentina'.
We book our tickets. Two days before our flight to Argentina he takes a job in Mexico. He's presently in Mexico in Sinaloa, which has a history about it, that area. It's a pretty tough part of Mexico - and he hasn't come out since!
I'm a big Martin Scorsese fan, and for me this film is a bit like Mean Streets.
It's got those elements of an early Scorsese film - lowlife gangsters everywhere you kind of go. Street guys, that's what they are. They're just trying to live and survive and do what they've got to do to make things happen. And that's who Diego Maradona is, and that's where he's from. For me Senna was like an all-out action hero on a spiritual journey. Amy's a very emotional musical, where the songs are the narrative in a way. And this is, I think if we're going to call it a genre, a kind of sporting gangster film.
Diego Maradona is in cinemas from June 14