Tracy Britt Cool

Ever since Warren Buffett hired Cool, the daughter of Kansas farmers, out of Harvard Business School in 2009, he has heaped responsibilities on her. He named her chairman of four Berkshire-owned companies (Benjamin Moore, Johns Manville, picture-framer Larson-Juhl, and Oriental Trading) and recently put her on the board of H.J. Heinz. "She's a blotter for learning," says Buffett.