Playboy magazine founder Hugh Hefner was an early gay rights advocate, a new film of his life claims.

The documentary, Hugh Hefner: Playboy, Activist and Rebel, says the 83-year-old, who is most famous for publishing images of naked women, has a little-known history of campaigning for equal gay rights.

In 1955, shortly after founding the magazine, Hefner published a short sci-fi story, The Crooked Man, by Charles Beaumont, in which homosexuality was the norm and heterosexuals were persecuted.

In response to the flood of angry letters he received, he wrote: “If it was wrong to persecute heterosexuals in a homosexual society, then the reverse was wrong too.”

According to a 2008 biography, Mr Playboy: Hugh Hefner and the American Dream, Hefner once had a gay sexual experience.

Author Stephen Watts claimed: “Hefner’s thirst for sexual experience became so strong that he even had a one-time homosexual experience.” The book was commended by Hefner as “the most authoritative book ever written about me”.

He has continued to support gay marriage, recently telling The Daily Beast: “Without question, love in its various permutations is what we need more of in this world.

“The idea that the concept of marriage will be sullied by same-sex marriage is ridiculous. Heterosexuals haven’t been doing that well at it on their own.”

The publisher, who has funded a number of legal battles for birth control and abortion rights, also said in 2002: “I was a feminist before there was such a thing as feminism.”

Hugh Hefner: Playboy, Activist and Rebel, is to premiere at the Toronto International Film Festival later this month.