Playboy Mansion Hosts Annual Halloween BashThe death of a cultural icon always leads to a wave of social media reactions, and Hugh Hefner's is no exception.

After news of the Playboy founder's death on Wednesday broke, celebrities quickly began paying tribute to him. They shared kind words, fond memories, and acknowledged his many accomplishments. Hefner was 91 when he died and was known for building an iconic media brand that challenged cultural norms and boundaries.

"He defined a lifestyle and ethos that lie at the heart of the Playboy brand, one of the most recognizable and enduring in history," Cooper Hefner, Hugh's son and Playboy Enterprises' chief creative officer, said in a statement Thursday. "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."

The reality TV contingent -- particularly those that had modeled for the magazine in the past -- was vocal on social media.

Hefner was also remembered for the way he changed our culture and supported social progress, including civil rights.

Still others shared stories about how they knew the man behind Playboy. We really wish we knew Kat Dennings's tale.

RIP, Hef.