ng-class billionaire, Ron Burkle, the mysterious 53-year-old who made his fortune in the very non-mysterious business of investing in supermarkets. Burkle—who also works with President Clinton—is a fixture at the Mercer Hotel, where he prefers to have breakfast and meetings when he's in town, instead o

he next ten years of profit from his Virgin Group's airline and train businesses in renewable-energy initiatives, worth $3 billion. Bing, along with Burkle and others, has pledged $1 billion to do the same. In June, Warren Buffett, the thrifty bridge player with the five-bedroom house in Nebraska, dona