Alan Greenspan, who started life as a shy, only child of a single mother, transcended the role of central banker, exercising extraordinary influence over American finance and commerce and enjoying unparalleled global stature during a period of remarkable prosperity. But by the time of his death, at age 100, the 2008-09 global financial crisis had recast his aura of technocratic omnipotence. Former colleagues and Nobel Laureate Milton Friedman hailed Greenspan as the greatest central banker of all time when he finished 18½ years as Federal Reserve chairman in 2006. Just two years later, the financial crisis triggered an austere reappraisal of his record. His view that…