Larry Fink built BlackRock into the largest investment firm in the world, with $4.6 trillion in assets under management. And two years ago he took it upon himself to redefine the relationship between the Fortune 500 and Wall Street. Fink wrote a letter to the CEOs of nearly every large company in America deploring the corporate culture of short-term thinking and threatening to vote out board members who didn’t hold management accountable. Other large investment firms have followed BlackRock’s lead—and Hillary Clinton adopted a tax proposal, similar to one Fink outlined, that would pressure shareholders to hold their investments longer. "If the system is really going to change, pressure needs to come from the investment community," says Rick Wartzman, senior advisor at the Drucker Institute. "And no voice has been more important or more forceful in this regard than Larry Fink's."