A gunmetal-gray BMW 745 Li sedan slips out of Steven A. Cohen's 14-acre walled estate. The chauffeured car races along the winding backcountry hills of ultrawealthy Greenwich, Conn. At around 8 a.m., it powers into the parking lot of SAC Capital Advisors. Cohen quickly emerges and darts into the front entrance of his gleaming steel and terra-cotta-slabbed Stamford (Conn.) headquarters. His driver swings the car around to the back and parks in a space with a simple reserved sign amid a sea of testosterone-exuding cars belonging to his traders: Mercedes S600s, Lexus sport-utility vehicles, and Porsche Carrera 4s. Cohen will soon be sitting at what one trader calls "command central" -- his desk with its numerous screens, perched in the midst of a football field-length trading floor. In the next few hours he is likely to earn several million dollars.
Cohen, 47, is the most powerful trader on Wall Street you've never heard of. The founder of SAC Capital Advisors, a highly secretive and stupendously successful $4 billion group of hedge funds that bears his initials, is considered to be a market genius by even his harshest critics. His firm routinely accounts for as much as 3% of the New York Stock Exchange's average daily trading, plus up to 1% of the NASDAQ's -- a total of at least 20 million shares a day. And while most of his rivals struggle to keep their trading costs down, "Stevie," as he's known on Wall Street, is one of the few to pay full freight. He hands over about $150 million a year in commissions to Wall Street, making him one of its 10-largest customers.