Hugh Hefner, the Playboy magazine founder who transformed the publishing industry by bringing sex and female nudity into the mainstream, has died.

He was 91. Playboy Enterprises Inc. said on Wednesday Hefner had peacefully died from natural causes at his home, the famed Playboy Mansion in Los Angeles.

While working at a children's magazine, Hefner put up $600 US to start Playboy, borrowing a few thousand from financial institutions and friends.

With a peak circulation of seven million and a strong brand identity, it became one of the most successful magazines ever.

Opposition from many quarters

When the company went public in 1971, his estimated worth was over $150 million.

What Playboy doesn't know about women could fill a book. - Gloria Steinem

Playboy magazine has survived into a seventh decade despite investigations and opposition from many quarters, including politicians, the FBI, the U.S. Securities and Exchange Commission, the U.S. Post Office, religious leaders and feminists.

So-called skin magazines had existed before, but Hefner said his approach was fresh — centrefolds were students, secretaries and stewardesses, not models or those on the margins of society.

Elsewhere, the magazine contained real journalism and espoused an aspirational philosophy of self-fulfilment and liberation from religious-based strictures.

'Removing some of the guilt'

"It is very important to me that we have played some part in the changing of sexual attitudes and the removing of some of the guilt that has been so very hurtful in our society related to sex," he told CBC in a 1983 interview.

Critics said Playboy presented an inadequate representation of female beauty, with real people negatively impacted by the unrealistic attitudes about women and gratification its airbrushed images fostered. If not pornography — and opinions varied — the magazine at minimum contributed to the oversexualization of the culture, it was charged.

Playboy publisher Hugh Hefner is pictured in the 1970s. (TIFF)

"What Playboy doesn't know about women could fill a book," feminist icon Gloria Steinem famously said.

Beginning in 1960, the brand was extended through a chain of Playboy Clubs, including one in Montreal. Casinos, hotels, a record label and a pay-TV channel would be among the company's ventures through the decades.

Circulation squeeze

The magazine has been battered by the advertising and circulation squeeze facing all print publications in recent years.

When a sale was rumoured in 2016, industry analyst Samir Husni argued, "The brand has no future because the reasons for its existence are no longer in place."

Hugh Hefner and his then-girlfriend Crystal Harris are shown in Los Angeles in 2013. (Matt Sayles/Associated Press)

Hefner's impact was possibly lost on younger generations who encountered him as the caricature he often resembled late in life, extolling the virtues of Viagra while engaging in transactional relationships with 20-something playmates, as in the popular 2005 reality show The Girls Next Door.

At one time, he had been viewed as prominent cultural critic on issues of free speech and sexuality.

Canadian women in his life

Hugh Hefner poses with "bunny girl" hostess Bonnie J. Halpin at Hefner's nightclub in Chicago in 1961. (Ed Kitch/Associated Press) Canadian women featured prominently in the magazine and in Hefner's life. About 20 have been playmates with four named Playmate of the Year: Dorothy Stratten, Shannon Tweed, Jayde Nicole and Kimberley Conrad, who was born in the U.S. but raised in Vancouver. Hefner dated Tweed, and in 1989 would marry Conrad, mother to his two youngest sons.

Those relationships came after the 1980 murder of Vancouver's Stratten by her ex-husband, which devastated Hefner and his staff.

Hefner was born April 9, 1926, in Chicago, to parents he described as emotionally distant. A child of the Depression, he sought with Playboy in "creating the party that I missed," he once admitted. His teen years had been fun but chaste; he didn't lose his virginity until 22.

With a degree in psychology and years spent scrapbooking and drawing cartoons, Hefner scuffled along professionally after a stint in the Army. He married in 1949 and daughter Christie arrived three years later, around the time Hefner made his entrepreneurial move.

Marilyn Monroe photo shoot

He obtained the rights to a nude Marilyn Monroe photo shoot for $200 for the inaugural December 1953 issue, which was an immediate sensation. The second edition marked the debut of Playboy's iconic bunny logo.

The company was grossing $20 million within a decade, a four-storey mansion in Chicago acting as its headquarters.

Newly divorced, Hefner would, for nearly three decades, unapologetically pursue pleasure in his free time.

In this 1983 interview, CBC's Barbara Frum poses some tough questions to Playboy founder Hugh Hefner. 11:32

"I guess I'm the most successful man I know," he said in the 1963 Canadian-produced documentary The Most. "Am I happy? I wouldn't trade places with anyone else in the world."

His image became entrenched — smoking a pipe and (especially after a mid-70s move to a 30-room Shangri-La in Los Angeles which he rarely left) wearing silk pajamas and bathrobe.

'Reading Playboy for the articles'

Hefner shaped the magazine to cater to his own interests and found a receptive audience in no small part due to a post-war baby boom and the sexual revolution brought on by the pill.

Playboy was a singular publication, but journalist Mike Wallace cut to the chase in an early TV interview: "Isn't that really what you're selling, kind of a high-class dirty book?"

This image released by Playboy shows the cover of the June 1965 issue. (Associated Press)

"Reading Playboy for the articles" became a sniggering popular expression, but true nudity comprised only 10 per cent of the pages. Ray Bradbury and Ian Fleming would help kickstart a literary tradition, with works featured over the years from the likes of Margaret Atwood, James Baldwin and Joan Didion.

The acclaimed Playboy Interview debuted in 1962; within just a few years it featured Ayn Rand, Malcolm X, Martin Luther King and Fidel Castro. U.S. presidential candidate Jimmy Carter confessed to "adultery in my heart" in a 1976 interview, causing a stir.

Championed racial equality

The magazine was a boon for high-end advertisers not shy with the adult association, targeting a professional, largely under-35 male demographic with automobiles, electronics and credit cards.

Hefner fought off an obscenity charge in 1963 and contributed money to the defence of jailed comedian Lenny Bruce. In its editorial pages, Playboy championed issues like racial equality, while staunchly opposing the Vietnam War.

Hugh Hefner conducts an interview in 1977. (George Brich/Associated Press)

But the ascendant women's rights movement took aim.

Steinem, who once donned a Playboy Club bunny costume as research for an article, grilled Hefner in a 1970 McCall's feature.

'You've made woman objects'

"Don't you understand that you've made woman objects, more easily exchanged than sports cars?" she said.

"I'm all in favour of women being able to vote, own property, and all that. But I want women to be attractive to men." Hefner countered, rather weakly.

Gloria Steinem, left, and Hugh Hefner, right, pose with former Life editor Byron Dobell at the U.S. National Magazine Awards ceremony in New York in 1998. (Peter Morgan/Reuters)

Erica Jong was slightly more charitable in a 1975 Playboy Interview: "No, I don't think they're being exploited, but they're not really women to me, they're almost figments of the imagination, sort of the apotheosis of the male mammary dream."

Hefner's hedonism in the 1970s took the form of celebrity-soaked sybaritic parties in the L.A. mansion's grotto or poker and movie nights with old cronies. It sounded like a dream to many subscribers but critics branded it an adolescent fantasy out of touch with the decade's tough economic times.

A trying decade

Hefner was often detached from Playboy's day-to-day operations, and Stratten's killing ushered in a decade that would be trying. Ill prepared, he made a disastrous appearance at a 1982 hearing in Atlantic City, leading to a casino licence being denied for a property already built.

Religious leaders emboldened by a conservative Republican winning the presidency ran campaigns that affected circulation and newsstand placement, and railed about Playboy at a federal commission on pornography.

Playboy founder Hugh Hefner, centre, poses with a group of current and former Playboy bunnies at the Playboy Club in Los Angeles in 1986. (Associated Press)

Hefner would suffer a stroke in the mid-80s.

The 90s were kinder as Hefner was able to be the attentive father he wasn't decades earlier, while adult daughter Christie streamlined the empire in her two-decade run as CEO. Playboy may have been staid, but it was closer to the very popular lad magazines like Maxim and FHM than the gauche stylings of Penthouse, or Hustler's gynecological bent.

Stigma decreased, but influence waned

The stigma to appearing in Playboy's pages in terms of a showbiz career decreased as Vancouver Island's Pamela Anderson and American personality Jenny McCarthy gained acceptance of a kind, but the magazine's influence on the culture waned.

The company went private again in 2012, and four years later a move away from nudity was trumpeted, then quickly abandoned.

Playboy Mansion parties had picked up again in the late 1990s when Hefner and Conrad separated. Hefner married a third time in 2012, and four years later sold the mansion purchased in 1971 for $1 million for a reported $100 million, staying there as a resident.

Interest in Hefner and his empire has resulted in a number of books and documentaries. American Playboy: The Hugh Hefner Story, a docuseries culled from thousands of hours of footage and hundreds of scrapbooks, debuted on Amazon in April.

Hefner's survivors include Christie and David, born to first wife Millie Williams, and sons Marston and Cooper from Conrad.