Warren Hellman, the philanthropist who founded the Hardly Strictly Bluegrass Festival in San Francisco in 2001, died Sunday (Dec. 18). He was 77 and had been battling leukemia. The annual free festival attracted 750,000 fans over three days in 2011. In addition, the portion of the Golden Gate Park where the festival is held was renamed Hellman’s Hollow this year. He built his fortune by heading Lehman Brothers in New York, by founding an investment firm that was an early backer of Apple Computers and by opening a money management business in San Francisco, Hellman & Friedman, one of the country’s most successful private equity funds. This year, Hellman toured with Jimmie Dale Gilmore in a country band called the Wronglers.