Aggressive, tenacious and litigious to a fault, Paul Singer may be the most feared activist investor in the world—by hedge fund rivals, companies and even countries. Singer’s Elliott Management Corp., which manages $34 billion of assets, has rarely been out of the headlines the past 18 months. And there’s little indication that will change soon. Singer has targeted the world’s biggest mining company, taken on Warren Buffett in a battle for Texas’s largest electricity distributor, ousted chief executive officers on both sides of the Atlantic and set off a chain of events that led to the impeachment of South Korea’s...