Hugh Hefner -- who founded Playboy and turned it into a globally iconic brand -- is dead at 91.

Playboy says Hugh died peacefully at home Wednesday, surrounded by loved ones.

Hefner's health had been in serious decline over the last year and he's not been seen in public for some time. His passing comes just over a year after his brother, Keith, died battling cancer.

Playboy magazine catapulted Hef into a cultural phenomenon ... paving way for the iconic Playboy Mansion that quickly became known for its legendary parties.

As TMZ reported ... Hefner parted ways with the pad in August 2016 ... selling to Pabst Blue Ribbon heir Daren Metropoulos for $100 million. But the sale had one condition -- Hefner could live in the mansion without the new owner's meddling until Hefner died.

Hefner married 3 times -- first to high school sweetheart Mildred Williams in 1949 ... then former Playmate of the Year Kimberly Conrad in 1989 ... and finally Crystal Hefner in 2012. She's 31.

His third marriage came 4 years after breaking up with longtime GF Holly Madison. He's survived by 4 children -- Christie and David from his first marriage and Marston and Cooper from his second marriage.

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Hefner founded Playboy in 1953 with Marilyn Monroe gracing the first cover. The magazine landed huge celebrities for years to come -- including Cindy Crawford, Kim Basinger, Pamela Anderson, Madonna, Sharon Stone, Naomi Campbell, Carmen Electra, Drew Barrymore and Kim Kardashian.

The magazine stopped publishing nude photos in 2016 but went back to them in February of this year after Hugh's son, Cooper, was named chief creative officer.