THE casting of Robert Downey Jr as Iron Man a little over a decade ago will go down as one of cinema’s greatest gambles.

At the time, the former Brat Pack star turned Oscar-nominee was persona non grata in Hollywood.

Despite being described as one of the most gifted actors of his generation, his struggles with drugs and alcohol, which led to stints in jail in the late ’90s, meant he couldn’t be insured for fear of a relapse. Without insurance, studios wouldn’t touch him.

But director Jon Favreau, who would kick off the Marvel Cinematic Universe with Iron Man, was adamant Downey was the man to play Tony Stark, a brilliant gadabout who has everything, but whose selfishness and arrogance lead to his downfall and incarceration and, ultimately, a shot at redemption.

Talk about art imitating life.

“It was interesting that the mythology of Tony Stark, if you kind of squeeze it down, is not entirely dissimilar to mine, except that he started from a much cooler place than I did,” Downey told the Sunday Herald Sun at the time.

Fast forward 10 years and it’s safe to say the gamble paid off — big time.

The MCU is the most successful film franchise in history with its 15 films so far taking a combined box office of more than $15 billion dollars. And thanks to the trailblazing role he played, despite the entry of other A-listers such as Chris “Captain America” Evans, Scarlett “Black Widow” Johansson, Chris “Thor” Hemsworth and Benedict “Doctor Strange” Cumberbatch, Downey is still unquestionably the big dog on the Marvel lot.

“The truth is, no one can take the leader role from Downey,” said Evans last year, when the two faced off in 2016’s highest grossing movie Captain America: Civil War.

“Downey is the reason this is happening. If the first Iron Man movies hadn’t worked, none of this would have happened. Downey is the patriarch. Everyone looks to him.”

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So when the time came to reboot and bring Spider-Man back into the MCU thanks to an unprecedented agreement between rival studios Sony and Disney, who better to make that introduction than the man who started it all?

Tom Holland, who stars as the web-slinger in Spider-Man: Homecoming, auditioned for his cameo in Civil War alongside Downey — and instantly became a fan.

“Robert is a really lovely, down to earth kind of guy,” the 21-year-old says of the man who acts as his mentor both on and off-screen. “He’s funny, he’s talented, he’s cool and he’s just a great guy to be around. He brings a very positive energy to set and makes everyone feel welcome. I am so grateful that he agreed to be in this movie because we really needed him to drive home the fact that we are bringing Spider-Man home to the MCU. He is the Godfather.”

Despite Holland’s general fan-boy freaking out upon meeting Iron Man, Downey says he has no intention of handing down wisdom from on high to the new kid on the Marvel block. He has his own memories of being schooled by industry veterans such as James Woods and says “there is no amount of advice you can give to someone if they are just inherently rotten”.

Downey describes Holland as “a really good dude” who is perfect to follow in the footsteps of Tobey Maguire and Andrew Garfield as friendly neighbourhood superhero Spider-Man.

“Tom is the perfect man for the job,” says Downey. “He’s enthusiastic, bright and gifted, a very physically talented guy by virtue of his dance and acrobatic background. He has just the right combination of elements required to bring a new take on the character.”

Despite being one of the highest paid actors in the world, Downey hasn’t headlined a film since his 2014 drama The Judge, which he also executive produced. His last solo Iron Man movie was the year before that, and although he has appeared as the character in a further five MCU films since, including the two Avengers movies being filmed at the moment, he gives the impression he’s happy to just be part of the ever-increasing ensemble.

Downey says his current working arrangements are “very conducive to having children” — married to producer Susan Levin since 2005, the couple have a five-year-old son and a two-year-old daughter. (Downey also has an adult son from a previous marriage.)

He’s also wary of outstaying his welcome. He empathises with the idea of superhero blockbuster fatigue and with no plans in place for an Iron Man 4 — and rumours that Stark might meet his maker in one of the two coming Avengers films — says he will only stick around as long as he is needed and as long as he’s engaged.

“It’s this cyclical thing,” Downey says. “I could have said when the first Avengers came out: ‘It’s never going to get any better than that. Everybody stop’. But to me it’s always about people and opportunities, like the (Avengers directors Anthony and Joe) Russos, who I adore.

“Everyone says to me it’s like a glove that fits so well. I have to start over every time but I am starting over with a pretty solid base. I just never want to blow it for the last six or seven (MCU movies) I have done by dropping the ball because I decided to go do it one more time. I just want to hang up my jersey before it’s embarrassing.”

At this point, Downey keeps coming back to Marvel because they keep coming up with quality. He was lured to Spider-Man: Homecoming because he liked what new director Jon Watts had done with his low budget 2015 film Cop Car.

“I felt like we were literally back in the writer’s room on the first Iron Man,” Downey says of making the freshy Spidey flick. “So there was a real sense of a homecoming toward this — not experimental, because there is so much more data now and the process is so much more streamlined — but I didn’t feel like I was being asked to just fit in somewhere. They wanted us to bring our own little thing.”

There was also the prospect of hanging out with Favreau, who went out on a limb all those years ago and once again acts alongside Downey Jr in Homecoming. Both relished being hired hands in a much bigger machine.

Like Downey, Favreau, who plays Tony Stark’s bodyguard Happy Hogan, has gone from strength to strength since the first Iron Man — his live action version of The Jungle Book grossed well over $1 billion last year. A sequel is in the works and he’s been enlisted to give the same treatment to The Lion King.

“Jon and I have been hanging out lately,” says Downey. “The big thrill for me is that he’s in this and I am excited because I just get to watch him as an actor. With the exception of Ben Stiller in Tropic Thunder, it’s really hard to be directing a movie and give a great, even small performance. He’s always giving himself a bit to do but this time it’s just Jon Favreau, original gangster and day player on fire. It gave me a whole new respect for how I originally remember him.”

SPIDER-MAN: HOMECOMING OPENS THURSDAY