Robert Downey Jr was only six years old when he took the first step on his chaotic path to drug addiction and prison.

His father had spotted him sipping a glass of white wine during a poker night at the family home in New York. But instead of swiftly extracting the glass from his young son’s hands, he passed him a cannabis joint and told him to puff on that instead. Such was cult film-maker Robert Downey Sr’s unorthodox approach to childcare.

Far less well known than his Hollywood-star son — who overcame his demons to become the world’s highest-paid actor — Robert Downey Sr was a maverick director who was also a hopeless drug addict for much of his life.

Years later, he admitted he had made ‘a terrible, stupid mistake’ in giving his six-year-old son drugs. However — as a new documentary, three years in the making, reveals — it was in keeping with a chaotic and irresponsible parenting style.

When he wasn’t handing his son narcotics, Downey Sr was taking little Robert off to watch X-rated films and even casting him — from the age of five — in his own disturbing and far from child-friendly movies. Home life involved ‘growing up in a family where everyone was doing drugs’, according to Downey Jr.

The younger of two children, Downey Jr was born in Manhattan, New York City, in 1965 and raised initially in the bohemian neighbourhood of Greenwich Village, where he says he was ‘surrounded’ by drugs at home

Is it any wonder, some might ask, that the future Iron Man star went off the rails so spectacularly?

He puts that very question to his ailing father in ‘Sr.’, a new Netflix documentary the star has made about his turbulent relationship with his father and his bizarre upbringing.

The film throws a revealing new light on a deeply troubled but self-assured actor who, in 1999, told a judge that, thanks to his father giving drugs to him, he’d been hooked since the age of eight. He added that his addiction to cocaine and heroin was ‘like I have a shotgun in my mouth, and I’ve got my finger on the trigger, and I like the taste of the gun metal’.

In July 2021, Downey Sr died aged 85 from Parkinson’s disease. Although they display a deep affection for each other — and Downey Jr avoids outright recriminations — the part his father played in his devastating personal problems is all too clear.

Referring to his dismal upbringing, Downey Jr says at one point: ‘I think we would be remiss not to discuss its effect on me.’

His father, embarrassed, mumbles back: ‘Boy, I would sure love to miss that discussion.’

The younger of two children, Downey Jr was born in Manhattan, New York City, in 1965 and raised initially in the bohemian neighbourhood of Greenwich Village, where he says he was ‘surrounded’ by drugs at home.

Robert Downey Jr was only six years old when he took the first step on his chaotic path to drug addiction and prison. He is pictured above in court in 1999

His parents were disciples of the 1960s counterculture and made underground films, his mother, Elsie, appearing in whatever her husband made — once playing all 12 of the female characters.

Although he influenced a generation of younger filmmakers, Downey Sr’s films were never commercially successful and the family lived hand-to-mouth in a cramped converted loft.

His father claimed he made an X-rated bonkbuster, The Sweet Smell Of Sex, only to pay the medical bills for the boy’s birth.

Robert Jr was only five when he had his first onscreen role. This was for an absurdist comedy, Pound (1970) — in which the cast played stray dogs waiting to be put down. Downey Sr typically made no allowance for five-year-old Robert’s age in the single line he scripted for him. ‘Have any hair on your balls?’ the boy asks a bald-headed man.

Two years later, a seven-year-old Downey Jr would appear in another of his father’s deranged films, a western called Greaser’s Palace. In this, his throat was cut by a Christ-like preacher and he had to watch as his own mother — also cast in the film — was viciously beaten.

The new documentary includes a clip of a rare interview, seemingly from the 1990s, in which Downey Sr admits: ‘A lot of us thought it would be hypocritical to not have our kids participate in marijuana and stuff like that. It was an idiot move on our parts to share that with our children. I’m just happy he’s here.’

Asked if he was ever worried that his son — who is next to him in the interview looking distinctly the worse for wear — might not survive, he replies: ‘Many times.’

The family moved at least a dozen times — to London, New Mexico, Los Angeles and Connecticut — as the parents pursued their careers at the expense of their children’s education.

In LA, family friends such as Jack Nicholson, Peter Sellers and Alan Arkin regularly visited a home where cannabis, Downey Jr says, ‘was a staple, like rice’.

In time, the director’s cult following drew the attention of the big Hollywood studios — and the family moved to California so he could make a 1980 comedy called Up The Academy. This depicted the outrageous antics of a group of misfits at a military college. It was a flop, but not before Downey Sr had tried to change the main characters to be ten-year-old children. The studio told him he was insane.

‘Some guy said: “If you keep talking like this, we’re going to fire you and you’re not going to get the final cut, no matter what happens,” ’ he recalls in the documentary. ‘I said: “OK, just as long as I get final cut on the cocaine.”

‘And that was almost the end of me out there.’

His son interjects: ‘You did not give a mad ****, did you?’

Eventually, says Downey Jr, drug-taking became the only way his befuddled father knew how to connect with him. ‘When my dad and I would do drugs together,’ he explained in a 1988 interview, ‘it was like him trying to express his love for me in the only way he knew.’

His parents divorced in 1978 — when Robert was 13 — and he initially moved with his father to Santa Monica, California.

At high school, his drug and alcohol problems escalated as he partied with the Hollywood brat pack. His fellow students there, including Sean Penn, Rob Lowe and Emilio Estevez, were already stars and Robert was determined to be one, too.

At 16, he dropped out of school to pursue acting. At 18, he was forced to fend for himself when his father cut him off financially.

Downey Jr returned to New York to try his luck on the stage. He swiftly found not only work but romance when — after a fling with future Oscar-winner Marisa Tomei — he began a serious relationship with fellow cast member Sarah Jessica Parker, then also 18, and some years from stardom in Sex And The City.

They lived together for five years before Downey Jr’s drug addiction destroyed their relationship.

By then, however, he had found his breakout role, playing — what else? — a drug-addicted rich kid in the 1987 film Less Than Zero.

The roles flooded in, including one co-starring with Mel Gibson in the 1990 action-comedy Air America, and an Oscar-nominated performance as Charlie Chaplin in 1992’s Chaplin. Downey Jr married model Deborah Falconer in 1992 and they had a son, Indio.

Meanwhile, his father’s second wife, actress and writer Laura Ernst — whom he married in 1991 — proved to be his salvation. He gave up drugs to look after her when she was diagnosed with motor neurone disease; she died aged 36 in 1994.

‘It was time to grow up, to think of somebody else first,’ he admits.

But there was no salvation yet for his son as his drug usage and chaotic behaviour only increased.

His father joked — with some cheek in the circumstances — that he kept track of his son by reading the scandal-packed National Inquirer.

There was plenty to report. In 1996, Downey Jr was arrested for speeding while drunk and possessing heroin, cocaine, crack cocaine and an unloaded gun. The following month, while awaiting trial, his neighbours called the police after discovering Downey Jr had wandered into their home in a druggy haze and passed out on their 11-year-old son’s bed.

The same year, his wife, Deborah, finally gave up on his drug-bingeing and left him. A judge ordered him to go into rehab. But he escaped, was recaptured and sent back, with Downey Jr admitting he was ‘the poster boy for pharmaceutical mismanagement’.

He repeatedly skipped court-ordered drug tests and was in and out of jail — twice waking in a pool of his own blood after other inmates attacked him — before a judge finally lost patience with the star’s entitled arrogance and jailed him for three years in 1999.

Even after getting out in 2000 and winning a Golden Globe for his performance as Calista Flockhart’s boyfriend in TV legal drama Ally McBeal, he continued to get into trouble. Police found cocaine and methamphetamine in his hotel room and, while on parole, he was found wandering around LA, barefoot and high.

Fired from Ally McBeal, he went back into rehab. Finally, in 2003, he met producer Susan Levin on a film set. She told him she would marry him — which she did in 2005 — only if he promised to quit drugs for good.

He went into therapy including a 12-step programme, took up meditation and kung fu, and now says the strongest drug he consumes is caffeine.

His film career never looked back. In 2008, Downey Jr was chosen to play billionaire inventor Tony Stark, alias Iron Man, in the first of Marvel Comics’ wildly successful Iron Man movies. The actor, who once earned 8 cents an hour scrubbing pans in jail, has made £355 million from the franchise.

It’s an astonishing tale of redemption — worthy itself of a Hollywood film. The question is, would any of it have happened if Downey Sr hadn’t given his six-year-old son that first cannabis joint all those years ago?