When Long-Term Capital Management, a big hedge fund, collapsed in 1998 and the price of many securities sank, Mr. Cohen pounced. From late August until mid-October, he stayed up late making bullish bets via the Globex 24-hour trading system, routinely arriving at the office with exhaustion etched on his face. For the year, SAC had returns of 49.2%, compared to an average of 2.6% among hedge funds, according to Hedge Fund Research...