Robin's hidden pain revealed by longtime friend

There didn't seem to be much that Robin Williams couldn't do. He spent a career entertaining us – making us laugh in The Birdcage and moving us in his Oscar-winning role in Good Will Hunting.

Williams used humour to bring others happiness, which made it all the more heartbreaking when the world learned of his apparent suicide at age 63. His publicist issued a statement saying Williams "has been battling severe depression of late. This is a tragic and sudden loss."

Yahoo News and Finance anchor Bianna Golodryga spoke with Jamie Masada, founder of the Laugh Factory and a long-time friend of Williams.

Masada works with many legendary comedians and knows firsthand the troubles some face off-stage.

"He's genuinely, genuinely one of those guys, such a high energy, we would never figure out anything. He would never let anybody get inside to know what was going on," says Masada.

"They don't want to talk about their problems. They always want to make people laugh."

Robin Williams with his wife, Susan Schneider and daughter, Zelda Williams. Photo: AP.

In 2011, Masada, with the help of psychologist Ildiko Tabori, started providing onsite therapy for performers at the Laugh Factory to help them cope with the highs and lows that often come with being an entertainer.

Mental health expert Dr. Jeff Gardere explained that depression and substance abuse among performers is more common than one may think, and Williams was no exception.

"He was a lifelong addict. It's a lifelong illness that you take a day at a time... this is a medical problem, and we have stop seeing people who have drug addiction as evil, bad, weak people," says Gardere.

Despite fame and fortune, celebrity artists may be more vulnerable to depression than the rest of us, brought low by the same creative qualities that gave them success in the first place, analysts say.

As tributes flowed in for comedian Robin Williams after his apparent suicide, there were many questions about the state of mind of the Oscar-winner once called the funniest man alive.

"Artists are often people who are more sensitive, who feel emotions more strongly," said Michel Reynaud, of the Paul Brousse Hospital's psychiatry department in Paris.

"This can yield great writers, poets and musicians, but also anxiety, depression, anguish and mood disorders," he told AFP.

Williams had suffered from depression, according to his publicist -- one more name on a long list of celebrity actors that includes Jim Carrey, Catherine Zeta-Jones and Stephen Fry who have battled the debilitating ailment.

The World Health Organisation (WHO) says more than 350 million people of all ages suffer from depression.

"Depression is different from usual mood fluctuations and short-lived emotional responses to challenges in everyday life," a WHO factsheet explains.

GALLERY: Robin Williams' most memorable roles. Photo: Supplied

*Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.