Neil M. Barofsky is not a household name like some special investigators of the past — Kenneth Starr during the Clinton administration or Archibald Cox in the Watergate years. But increasingly, Mr. Barofsky is setting off fireworks on Capitol Hill as he quietly and methodically pieces together the most complete historical record yet of the financial bailout. His reports are careful but not cautious, showing a willingness to stand up to some of the most powerful people and institutions in Washington or on Wall Street.