The Federal Reserve chairman — an economist and a disciple of libertarian icon Ayn Rand — met his first major challenge in office by preventing the 1987 stock-market crash from spiraling into something much worse. Then, in the 1990s, he presided over a long economic and financial-market boom and attained the status of Washington's resident wizard. But the super-low interest rates Greenspan brought in the early 2000s and his long-standing disdain for regulation are now held up as leading causes of the mortgage crisis. The maestro admitted in an October congressional hearing that he had "made a mistake in presuming" that financial firms could regulate themselves.