Bill Ackman is one of the most widely followed investment managers in the world. He's in charge of Pershing Square Capital, a hedge fund focused on investing in just a handful of Ackman's best ideas. His highly concentrated portfolio is full of great companies, but he might have just made one stock the biggest holding at Pershing Square.

Go big or go home. Billionaire investor Bill Ackman of Pershing Square Capital Management takes that sentiment to heart. His hedge fund has some $13 billion in assets under management, but he owns just 10 stocks (track his portfolio here),

Billionaire investor Bill Ackman's Pershing Square Capital acquired a $2.3 billion stake in Uber by purchasing 30.3 million shares. Ackman has praised Uber's CEO for transforming the company and also claimed that the company has more scope for growth.