San Francisco financier and philanthropist Warren Hellman died Sunday at the age of 77, according to his family.

Hellman, founder of private equity firm Hellman and Friedman LLC, championed a wide variety of ventures and causes. However, for many he was best known as the founder of the hugely popular Hardly Strictly Bluegrass music festival in Golden Gate Park and more recently as chairman of the board for the Bay Citizen, a nonprofit news organization he helped found in 2010.

"Warren was a great mentor, partner and friend, and above all, a great man," said Brian Powers, Chairman of Hellman & Friedman, in a press release posted on the company’s website. "He will be deeply missed. His commitment to civic and philanthropic activities and his extraordinary generosity to the many causes he supported will have a lasting impact on our community."

Jonathan Weber, the Bay Citizen's founding editor-in-chief, said the news of Hellman's death came as a shock. He described Hellman as a "quirky" man who did things his own way and questioned the conventional wisdom.

"He was an outstanding chairman, he really gave a lot of himself, both money and otherwise, to make the Bay Citizen happen," said Weber, who left the Bay Citizen in September. "His commitment to journalism was very real and I think everyone on the editorial staff felt that."

Hellman was also actively involved in city politics, and mayor Ed Lee this evening called him "a great friend, true hero and one of a kind San Franciscan."

"Few have contributed so much of their heart and soul to improve our city, leaving a legacy that will endure forever," Lee said.

San Francisco city officials on Thursday renamed Speedway Meadow in Golden Gate Park, the site of Hellman's free annual bluegrass and music festival, as Hellman Hollow. Hellman was a lifelong music lover who played in the bluegrass group The Wronglers.