Tommy Wiseau was a mysterious, eccentric, struggling actor who wanted to make the greatest movie of all time. He made the one of the worst – and it’s now become a cult classic exactly because of its flaws.

Director James Franco was drawn to the sheer wackiness of the story of Wiseau and his film The Room, and thus The Disaster Artist was born. An adaptation of a book by Greg Sestero, Wiseau’s friend and The Room co-star, the tale subverts the usual Hollywood biopic. Genre conventions invariably have a genius struggling to have his talents acknowledged, before finally being celebrated. The Disaster Artist, however, centres on a character who possibly doesn’t have any talent yet succeeds – albeit in a different way than anticipated.

“Tommy set out to make this serious drama and win awards,” explains Dave Franco, who plays Greg Sestero. “Ultimately, he achieved his goal of becoming famous, but in the most unlikely fashion. It’s a strangely inspiring story, because he persevered – but obviously it’s very weird, too.”

The Disaster Room recounts how Tommy Wiseau and Greg Sestero became friends, and then the outrageously unorthodox production of The Room – and the unorthodox nature of Tommy Wiseau himself. A mysterious figure who constantly conceals how old he is, where he’s from, and where he made the $6 million he spent on making The Room, there’s an even bigger mystery at the heart of Tommy Wiseau’s identity: does he really believe that he’s talented? How?

While James Franco’s portrayal of the affected and eccentric Wiseau is hilarious, it’s also a subtly complicated portrait of friendship, ego and the American Dream.

When Tommy ambushes a Hollywood director in a restaurant and painfully misquotes monologues, or when he tries to convince a bewildered acting coach that – despite his vampirish, aged looks and Eastern European accent – he is the All American Hero, the audience experiences a painful mix of humiliation, empathy and cynicism. Yes, Tommy is often treated harshly. But for someone with that lack of talent and level of delusion, is it kind to be cruel?

It’s a struggle faced by Greg Sestero, and a question Dave Franco asked Sestero during his research.

“I spent a lot of time with Greg before shooting,” reveals Franco, “so that I could understand what drew him to Tommy in the first place, and whether, while filming The Room, he thought it could be any good. He claims he didn’t, but as a young actor, I dunno – there’s something about just being on a movie set.”

Though known both as the brother of James and the star of Scrubs, 21 Jump Street, Now You See Me and Neighbours, Franco – like all young actors – struggled in the early stages of his career.

“As a young actor, you’d rather be the lead in the worst movie ever,” he says, “than the manager of the greatest retail store in the world. As an actor, you just want to act. So even when everyone else can see that a project is not good, you have to believe that it could be something special – that it could help progress your career. I’ve been on many movie sets where I thought the movie was going great, I thought we were going to get awards. And then the movie comes out – and not only is it not great, it’s really, really bad! That’s the crazy thing about our business – you can go in with all the right people and have all the best intentions, but you really never know how it’s all going to turn out.”

Greg meets Tommy when they’re both struggling actors. While Greg is good-looking and charming, he’s shy and inhibited, and also too broke to move to Los Angeles and really pursue acting. When he meets the uninhibited Tommy, he wants to learn how to develop that confidence – and when Tommy offers to fun their move to LA, he accepts.

In some ways, Greg could be viewed as using Tommy, but Franco thinks Greg was more innocently motivated.

“As crazy as Tommy seems on the surface,” says Franco, “he’s also very uninhibited, and he’s everything that Greg is not. So Greg is attracted to that. They’re both dreamers, they both want to be actors, so they really lean on each other for support when no-one else in their lives believes in them. It’s only later that Greg starts to wake up and realise, ‘I guess it is kind of weird that I don’t know how old he is, or where he’s from, or how he got the money to make the movie!’”

The film is about the personal and working relationship between Tommy as a director, and Greg as both his actor and friend – a dynamic that Dave and James Franco could understand, working together for the first time. Thankfully, their experience working together on The Disaster Artist was much less rocky – and resulted in a far better film.

“This is the first full-on project that James and I have worked on together,” enthuses Franco. “It’s been really fun! He’s a great actor’s director, in that he puts a lot of time into casting the right people in each role, and then he’s pretty hands-off. He lets the actor go with their instincts. On set, when he’s behind the camera, he’s the happiest I’ve ever seen him, he’s like a little kid. And his portrayal of Tommy Wiseau is pretty unbelievable, literally the role James was born to play – I don’t know what that says about him!”

The Disaster Artist is out now.