He was trained formally at the Juilliard School, the prestigious US talent academy founded a century ago. But in a career spanning four decades, comedian and actor Robin Williams came to personify the very opposite of its rigid, classical tradition.

The 63-year-old film and television star, who died at his home in Tiburon, California, was simply a force of nature: an unrestrained, chaotic performer whose genius and madness was there for all to see, as the alien Mork from Ork, as the inspirational teacher John Keating in Dead Poet's Society, as Aladdin's animated genius or as the strict modern-day Mary Poppins, Mrs Doubtfire.

Each performance, and countless more on what became a vast and varied body of work, was inexorably seared into the cultural memory of successive generations, catapulting Williams to the status of a film icon and, on a more intimate level, a man whose boisterous laughter and twinkling eyes seemed to reach through the celluloid and touch us all.

But in his manner, and in his comedy, and, sometimes, in the deep wells of his eyes, there was a glimpse of the inexplicable sadness, that thing some people call the tears of a clown. And behind it, perhaps, a hint of the darkness that would ultimately consume him. Marin County's sheriff's office said it suspected "the death to be a suicide due to asphyxia".

Williams' publicist Mara Buxbaum confirmed he had been batting "severe depression". And Williams himself spoke openly about his addiction to alcohol and drugs, and his relapse after two decades of sobriety. "You're standing at a precipice and you look down, there's a voice and it's a little quiet voice that goes, jump," he said.

Williams death struck a powerful chord around the world, triggering a reaction that seemed reserved for very few. His third wife Susan Schneider seemed to capture the mood perfectly in a short statement: she was "utterly heartbroken," she said. "I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings."

The immediate and very personal reaction, from friends, peers and fans around the world, was a demonstration of the telling nature of Williams' celebrity: not remote and manufactured, like many Hollywood stars of his generation, but spontaneous and fabulous. Like many comedians, the pathos in his words, aimed with precision, talked to us powerfully and individually.

At his star on Hollywood's Walk of Fame and, curiously, more than 1600 kilometres away at the Boulder, Colorado, house that served as the fictitious exterior of the home Mork and Mindy shared in the sitcom Mork & Mindy, garlands of flowers and candles were left in tribute.

So, too, an outpouring of grief from those who knew him, and those who did not. He was one of a kind, said US President Barack Obama. "He arrived in our lives as an alien but he ended up touching every element of the human spirit. He made us laugh. He made us cry. He gave his immeasurable talent freely and generously to those who needed it most."

Australian director Phil Noyce described Williams as a "force of nature". Director George Miller, who worked with Williams on Happy Feet, spoke of his profound humanity. "He had a huge heart and that intelligence you saw in his humour was in his normal conversation," Miller said. "In every way, it will be a deeply felt absence."

"Famously kind, ferociously funny, a genius and a gentle soul," said Michael J. Fox. "Great talent, acting partner, genuine soul," said Steve Martin. TV comedian Mindy Kaling, whose parents named her after the latter half of Mork & Mindy, said: "He meant so much, to so many, so far away." Film star Danny DeVito could only manage a single word: "Heartbroken."

As fans, what we will ultimately remember is Williams at his very best: the madness and the brilliance, and the mischief and misbehaviour. For a generation of Australians, Williams will forever be the man who reduced Australia's "perfumed steamroller" Jana Wendt to fits of laughter by meeting her desire to conduct a serious interview head on with persistent, unrelenting humour.

Though we have lost the man, Hollywood, perversely, is not yet done with the recorded image of him. Williams left behind three unreleased films, November's Merry Friggin’ Christmas, December's sequel to Night at the Museum, Secret of the Tomb, and next year's Absolutely Anything.

More tangibly, he leaves behind three wives and three children: Valerie Velardi and son Zachary, now 31, Marsha Garces and daughter Zelda and son Cody, now 25 and 23, and his current wife, Susan Schneider.

He also leaves behind, in actress Pam Dawber, an on-screen wife Mindy. Their partnership launched his television career, he as the eccentric alien Mork, a role that, despite an Oscar, two Emmys, four Golden Globes and five Grammys, he never seemed to leave fully behind. To her, perhaps, we leave the last word: "I am completely and totally devastated," she said. "What more can be said?"