For years, whenever anyone asked Raj Rajaratnam about the success of his hedge fund, the Galleon Group, he chalked it up to being hungrier than everyone else. "It is pride, and I want to win," Mr. Rajaratnam said in "The New Investment Superstars," a book by Lois Peltz published in 2001. "After awhile, money is not the motivation. I want to win every time. Taking calculated risks gets my adrenaline pumping."

Now prosecutors are claiming that Mr. Rajaratnam, 52, crossed the line into criminal activity.

At dawn on Friday, Mr. Rajaratnam was arrested at his expensive Manhattan home, charged with running the biggest insider trading scheme involving a hedge fund. He and five others are accused by the Justice Department and the Securities and Exchange Commission of relying on a vast network of company insiders and consultants to make more than $20 million in profit from 2006 to 2009. Mr. Rajaratnam's lawyer has said his client is innocent. He is free on $100 million bail and is expected to be in the office Monday to address Galleon employees.

In 2007, Mr. Rajaratnam's name arose in connection with an inquiry into fund-raising for the Tamil Tigers, the Sri Lankan rebel group that was defeated in May after a quarter-century of violence.  News of Mr. Rajaratnam's arrest has also shaken the secretive hedge fund world, in which intelligence on companies is often shared among Wall Street analysts, traders and other investors.

"The defendants operated in a cozy world of `you scratch my back, I'll scratch your back,' " Preet Bharara, the United States attorney for the Southern District of New York, said on Friday. He added that the case should be a "wake-up call" for hedge fund managers who even think about insider trading.