Former Federal Reserve Chair Alan Greenspan has become an adviser to a New York hedge fund that has made billions of dollars on the subprime mortgage crisis. The firm, Paulson & Company, made an estimated $15 billon by making aggressive bets against subprime home loans. The Wall Street Journal reports the head of the fund John Paulson made an estimated three or four billion dollars last year – it is believed to be the largest one-year payday in Wall Street history.