Playboy magazine founder Hugh Hefner died from natural causes at 91 years old on Wednesday, RadarOnline reported.

The men’s magazine mogul “peacefully passed away today from natural causes at his home, The Playboy Mansion, surrounded by loved ones,” Playboy spokeswoman Teri Thomerson told Radar.

“My father lived an exceptional and impactful life as a media and cultural pioneer, and a leading voice behind some of the most significant social and cultural movements of our time in advocating free speech, civil rights, and sexual freedom. He defined a lifestyle and ethos that lie at the heart of the Playboy brand, one of the most recognizable and enduring in history. He will be greatly missed by many, including his wife, Crystal, my sister, Christie, and my brothers David and Marston, and all of us at Playboy Enterprises,” said Cooper Hefner, Chief Creative Officer of Playboy Enterprises.

Aside from becoming a legend for featuring beautiful, scantily-clad women in Playboy, which was first published in 1953, Hefner used the magazine to advocate civil rights, sexual freedom, and free speech. In fact, he's been called a revolutionary for his promotion of African American activists and entertainers—including Martin Luther King Jr., who did his longest print interview with Playboyaccording to The Daily Beast.

Plenty of his famous friends are paying tribute to him on social media:

And as our tribute to his storied life, here are some of our favorite photos of Hefner.