Activist investing takes places in even the largest multinational firms, as was the case with Bill Ackman of Pershing Square Capital Management, who forced McDonald's ( MCD) to make vital changes to its menu, improve customer service and realize hidden real estate value, all of which ultimately led to a doubling in McDonald's stock price.Another large multinational firm engaged with an activist investor is Yahoo! ( YHOO). Now-board-member Carl Icahn has so far been unsuccessful in his attempts to get Yahoo! to sell its search business -- or even the entire company -- to Microsoft ( MSFT). But sometimes the activist investor isn't just another hedge fund. Take GSI Group ( GSIG). Stephen W. Bershad, the CEO of Axsys Technologies ( AXYS), put his own capital on the line when he recently bought 3.3 million shares of GSI Group in the open market. To read more, visit Stockpickr.com. Editor's note: David Peltier will be on Stockpickr Answers today to respond to questions posed by members of the Stockpickr community. Not a member? Join the Stockpickr community today - for free.