Robin Williams used to grope his Mork & Mindy co-star Pam Dawber as his madcap sense of humor crossed the line into sexual harassment, a new book reveals.

In the upcoming biography of the comedian, Robin, by New York Times journalist Dave Itzkoff, Dawber, 66, tells how the actor repeatedly grabbed her bottom and breasts and took off his clothes in front of her during the four-year run of the show.

Williams would also wrestle her down and break wind on her, and once 'goosed' an elderly actress playing her grandmother by putting a cane between her buttocks, she disclosed.

But the actress, who played Mindy alongside Williams's Mork, admits that she never took offense because the comedian was so charming.

She described filming the show as 'so much fun' and remarked: 'It was the Seventies, after all.'

Mork & Mindy: Actress Pam Dawber has revealed that she had 'the grossest things' done to her by co-star Robin Williams on the set of their hit show

No offense taken: Dawber (pictured in 2015) however, who played main character Mindy, admitted that she was unfazed by Williams's antics because the comedian was so charming

The show's director Howard Storm also contended that there was 'nothing lascivious about it, in his mind, it was just Robin being Robin.'

However, the revelations about Williams, one of the most adored comics of all time, could cause consternation for some of his fans and those of the show which ran from 1978 to 1982.

Dawber's unfazed reaction may surprise some too as it comes amid the MeToo movement, when victims of sexual harassment are encouraged to speak out.

Itzkoff interviewed Dawber for the book - set to be released in May and published by Henry Holt. It is the most thorough account of the comic's life since he hanged himself in 2014 after being diagnosed with Parkinson's.

The autopsy on his body revealed he also had Lewy bodies, a nerve condition which causes dementia.

The TV sitcom made a star of Williams and kicked off his Hollywood career that would include films like Mrs Doubtfire and Dead Poets Society, which made him one of the most famous comics on the planet.

In the show, a spin-off of the television hit Happy Days, he played an alien who comes to Earth from the planet Ork and moves in with a roommate, Mindy.

Dawber, who played a human who would eventually become Mork's wife, gave Williams a springboard for his wild, offbeat humor.

Speaking to Itzkoff, Dawber said Williams was 'such a nice person' and had a 'gigantic heart,' adding that they became close and she became the big sister that he never had.

'I really loved Robin and Robin really loved me. We just clicked,' she said.

Williams and Dawber starred together on the show from 1978- 1982. Williams played an alien, Mork, who came to Earth and moved in with Mindy. Dawber, who played a human who would eventually become Mork's wife, gave Williams a springboard for his wild, offbeat humor

The comedian's role on the show kicked off his career in Hollywood which eventually saw him win an Oscar in 1997. Above he is pictured after accepting his Golden Globe in 2005

But on the set Williams did things that went beyond those which a brother and sister would do to each other, ranging from crass behavior, to sitting and farting on Dawber despite her protestations.

Williams, however, also caused tensions on set with his constant improvisations which led some to think there was no script, a myth he perpetuated.

Itzkoff writes that many of these additions were sexual and directed at the women in the cast, such as when he goosed the actress who played Mindy's grandmother with a cane.

Storm said: 'I'm standing there watching this and I'm thinking, "oh my god" and I just laughed. I thought she was going to turn and say: "How dare you stick a cane in a woman's a**?" That sweet old lady.

'There was nothing lascivious about it, in his mind. It was just Robin being Robin, and he thought it would be funny. He could get away with murder.'

Other times Williams would grab Dawber's bottom or her breasts simply because he was 'bored.'

'He'd be doing a paragraph and in the middle of it he would just turn and grab her a**. Or grab a breast. And we'd start again. I'd say, "Robin, there's nothing in the script that says you grab Pam's a**." And he'd say: "Oh, ok,"' Storm added.

Garry Marshall, the producer of the show, said: 'He would take all his clothes off, he would be standing there totally naked and she was trying to act. His aim in life was to make Pam Dawber blush.'

But Dawber remained unfazed, she admits: 'I had the grossest things done to me - by him. And I never took offense. I mean I was flashed, humped, bumped, grabbed. I think he probably did it to a lot of people...but it was so much fun.

'Somehow he had that magic. If you put it on paper you would be appalled. But somehow he had this guileless little thing that he would do - those sparkly eyes. He'd look at you, really playful, like a puppy, all of a sudden. And then he'd grab your t*ts and then run away. And somehow he could get away with it. It was the Seventies, after all'.

Friends: One of Williams's mentors was comedy legend Richard Pryor (pictured in 1995) whom he met in the early 1970s at The Comedy Store in LA - where he'd begin an 'enduring pattern of behavior', staying up late until sunrise doing drugs and drinking with other comics

Williams had studied at the Julliard School in NYC where he met Christopher Reeve, the Superman actor who became a lifelong friend. Reeve died in 2004

Mork & Mindy changed Williams's life incalculably and by the time it finished in 1982 he had gone from never having had a gig that lasted more than three weeks to a national star.

But his success came with a cost as his marriage to his first wife Valerie Velardi - whom he married in 1978 - became strained due to his constant work and cocaine-fueled partying with the comedy crowd.

In fact, fellow comics would say 'Robin loved cocaine.'

During one of his performances at the Comedy Store, Valerie was in the audience when he said: 'There's girls that come up to me and they're like: "Excuse me, would you?" and pointed towards his crotch.

Valerie shouted out: 'Oh, you love it,' to which Williams responded: 'Oh, now my wife's heckling me'.

Itzkoff writes that Valerie had 'no illusions' about her husband's drinking, drug use, and infidelity but 'had to allow him these indulgences in the hope that his waywardness was providing him with something that he needed as an artists and performer.'

If you put it on paper you would be appalled. But somehow he had this guileless little thing that he would do - those sparkly eyes. He'd look at you, really playful, like a puppy, all of a sudden. And then he'd grab your t*ts and then run away. And somehow he could get away with it. It was the Seventies, after all.

They would remain together until 1988 by which time they had a son, Zak.

Williams's drug use escalated further, but the death of fellow comedian John Belushi from an overdose in 1982 caused him to sober up - he would remain clean for two decades.

After a few false starts, Williams's movie career took off with Good Morning Vietnam in 1987 in which he played renegade DJ on a military radio station in Saigon during the Vietnam War.

His improvisational style for the rapid fire scenes made the film a massive hit.

In 1989, the year after Williams divorced Valerie, he married Marsha Garces, Zak's nanny, who took a far more active role in his life by managing his schedule and acting as his gatekeeper.

Their marriage was the most stable and most successful period of Williams's life and resulted in classic hit films such as Good Will Hunting, which earned him the Oscar for Best Supporting Actor.

There were also beloved children's movies such as Jumanji, Flubber, Hook, and the voice of the genie in Disney's Aladdin.

Williams and Marsha had two children, Zelda and Cody, and in one interview he had said that thanks to his wife he found peace and 'stopped running around with all this madness.'

Marsha dismissed the idea she was his savior and said: 'He needed stability. I'm Robin's safety net. He knows I'm strong.'

Born on July 21, 1951, Williams grew up between Michigan and Illinois as his father moved around and climbed the corporate ladder at the Ford motor company, which made it hard for him to make friends.

The comedian married his first wife Valerie Velardi (pictured in 1979) but his success as an actor strained his marriage due to his constant work and cocaine-fueled partying with the comedy crowd. The marriage produced a son, Zak

The year after Williams divorced Valerie, he married Marsha Garces, with whom he had two children, Cody (far left) and Zelda (second from right)

Instead he lived in his imagination; for a time the family lived in the Stonycroft mansion in Detroit, where he would spend hours in his attic playing with his vast collection of toys and creating characters in his head, acting them out in his own private fantasy land.

Itzkoff writes that Williams would 'in a sense never leave the attic' and would spend his entire life surrounded by fictional friends.

Williams attended Claremont Men's College in Los Angeles where he planned to become a foreign service officer but took a theater elective class and after that he was 'hooked'.

He moved to New York where he studied at Julliard where he met Christopher Reeve, the Superman actor who became a lifelong friend, but he did not finish the course.

Williams relocated to Los Angeles and began performing at the Comedy Store where future stars like David Letterman had checked him out. Williams met comic legend Richard Pryor, his comedy mentor, and became friends with him.

It was here that Williams began an 'enduring pattern of behavior', staying up late until sunrise doing drugs and drinking with other comics, that would haunt him his whole life.

Marsha, his second wife, helped to keep him straight until the 2000s when he suffered a series of personal losses.

Reeve died in October 2004 to a pressure wound caused by being bound to a wheelchair as a result of a horse riding accident nine years earlier.

Pryor died the following year and Williams began drinking again for the first time in 20 years and thought about committing suicide.

After a family intervention in 2006, he detoxed at the Hazelden Foundation center in Newberg, Oregon followed by months of Alcoholics Anonymous, but his relationship with Marsha was never the same since he had kept his drinking secret from her.

Family drama: Williams married his third wife Susan Schneider (pictured) in 2011 after having met her in an Apple store in 2007. However, his family believed the two actually met at AA. An ugly legal dispute began between Susan and Williams' children over the comedian's estate

Itzkoff describes it as a 'catastrophic breach of faith by the person she was supposed to be able to trust completely.'

'The revelation of his relapse poisoned their marriage and cause her to question everything she knew and took for granted about him,' Itzkoff writes.

As Zak puts it: 'He had been married most of his adult life...when fame hit, it hit really hard. It was nonstop from 27 years onward. It was just a ride. It's only when things slowed down a bit that he could assess the situation'.

At the end of 2007 Williams and Marsha split up. His film career was failing and that year his half-brother Todd, a figure he thought of as 'immortal', died of heart failure at 44.

After divorcing Marsha, Williams moved to Tiburon near San Francisco where his father had moved his family when he was a teenager, seeking privacy and comfort.

His house had a bunker with no windows in which he kept collections of soldiers from every war he could find. There were lead ones, Japanese ones, German ones, soldiers from the Boer War – a colonial British conflict in South Africa at the turn of the century - and lots of Star Wars memorabilia.

'I think they were his friends,' his friend Lisa Birnbach said.

Williams occasionally did stand-up comedy and, with two ex-wives and alimony to pay, he embarked on a tour called Weapons of Self Destruction in late 2008.

But in early 2009 when he reached Florida, he developed a nagging cough and started feeling dizzy. He was examined by a doctor who told him he had an irregular heartbeat and damaged heart valves which he decided to have replaced.

Just before the operation at the Cleveland Clinic, his family were introduced to his new girlfriend, Susan Schneider, a 44-year-old artist and graphic designer, who had been on tour with him.

He told his family they had first met in October 2007 at an Apple store and had been quietly dating while Williams's divorce from Marsha was still ongoing.

But Zak felt differently and thought that the two actually met at an AA meeting - Susan was a recovering alcoholic who had been sober for 23 years.

Itzkoff writes: 'Amid the anxiety and uncertainty of whether Robin would even survive the surgery or his recovery from it, his children were concerned that Susan was monopolizing their father.

'In a particularly awkward moment, Robin's surgeons offered his family a pager to hold on to during the procedure which could be use to summon them on a moment's notice if any problems occurred.

'While Zak and Cody hesitated, each expecting the other to take the pager, they were startled when Susan claimed it for herself.'

Zak said that Susan 'expliciting expressed a disinterest' in getting to know them as people' and that they were 'hurt' by her conduct.

In 2011 Williams and Susan married at a ceremony in Napa Valley but it was a 'fraught' affair for his three children, according to Itzkoff, because they felt loyal to Marsha and were not sure if they should even be there.

While some of Williams' friends thought that Susan gave him companionship he sorely needed, others noted that she did not manage his affairs like Marsha did.

She did not always go with him when he worked out of town and had a life on her own, traveling widely by herself and spending time with her two sons from a previous marriage.

From 2013 onward Williams's health got worse and he began to have stomach cramps, tremors in his left arm, and he walked with a stoop at times. His anxiety and nervousness took over his life.

A year later, he was diagnosed with degenerative Parkinson's disease which attacks the central nervous system and eventually leads to death.

Williams's children decided to spend as much time with him as possible but that meant getting around Susan, his assistant Rebecca and his managers - this 'resistance' discouraged them from seeking him out.

Zak worried that his father was isolated and became concerned when he told him Susan was making him hang out with her friends who he was 'deeply suspicious'. 'They feel like users,' he told his son.

In June, Williams checked himself into rehab again in. His stay at the Dan Anderson Renewal Center in Minnesota would keep him where he could manage his illnesses, Susan thought.

The tell-all biography on the one of the most adored comics of all time will be released on May 15

But other friends saw it differently, Itzkoff writes, and that Williams had 'no reason' to stay at a rehab clinic when he was suffering from a physical disorder.

Close friend Wendy Asher said: 'That was wrong. This was a medical problem. Susan thought everything could be fixed through AA, and it just wasn't true.'

Weeks later Williams banged his head on the bathroom door, causing it to bleed heavily. Susan later said the injury led him to enter 'trance-like states' and become 'frozen'.

Friends said that he had a 'thousand-yard stare' and did not recognize him.

On August 9, Williams visited Zak and Alex who half jokingly asked him to stay with them. Zak said: 'We didn't want someone who seemed to be in so much anguish to leave. We wanted him to stay with us. We wanted to take care of him'.

The next day Williams was at home with Susan when he began to 'fixate' on some of his designer wrist watches and became paranoid they were in danger of being stolen.

He stuffed some of them in a sock and around 7pm drove to his friends Rebecca and Dan Spencer nearby and gave the watches for safekeeping.

He said 'goodnight my love' as he always did to Susan and offered her a foot massage which she declined.

He rummaged through the bedroom closet and left with an iPad which Susan saw as a good sign because she thought he was reading.

He left her bedroom at 10.30pm and headed to the separate bedroom he slept in.

At 11.42am the next day his assistant, Rebecca, used a paper clip to force open the door and made the horrific discovery: Williams had hanged himself with a belt.

Susan later revealed that she said goodbye to her husband that afternoon and told him: 'I'm not mad at you, I don't blame you at all. You fought so hard and you were so brave.'

The autopsy report from the Marin County Coroner confirmed that Williams had Lewy bodies, which Williams did not know about during his lifetime.

More surprises were to follow with regards to Susan.

A month before he married Susan in 2011 Williams had entered into a prenuptial agreement with her which said he planned to leave his $100 million estate in a trust which was operated by his attorneys.

He also created a separate trust for Susan worth $7 million and their Tiburon home, its contents and enough cash to cover her day to day expenditure.

Williams however said that specific items like his memorabilia and personal items should go to his three children.

An ugly dispute began between Susan and Williams' children which ended up in court.

Susan accused the Williams children of taking things they were not entitled to while they accused her of refusing to give them their father's belongings.

Both sides eventually came to an agreement under which Williams' children would get thousands of items like his Oscar statue, 50 bikes, and 85 watches. Susan received enough money to remain in the home they had shared for the rest of her life.

Itzkoff writes that the whole dispute 'reinforced a long standing discomfort they had felt about Susan, and whether she fully shared the values of her husband and his family.'

Cheri Minns, Williams's makeup artist, said: 'I think she just wanted to secure her place as Mrs Williams - the final Mrs Williams. And to always be that. I can't see that. And none of it really matters. Because he's gone'.

Zak said: 'Susan was under the impression she had struck gold. But for us, we're deeply involved with Dad's life. You can't untether us from the equation.'

David Itzkoff's Robin will be released on May 15, 2018 and is available for pre-order on Amazon.com