For years, whenever anyone asked Raj Rajaratnam about the success of his hedge fund, the Galleon Group, he chalked it up to the determination and intelligence of his staff.

"It is pride, and I want to win," Mr. Raj 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 puming:"

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

At dawn on Oct. 17, 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 in his 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. To gain an edge, hedge funds use lobbyists, private investigators and other connected people to dig for information about a company or industry.

While most of the information is obtained legally, the government’s use of wiretapping and confidential witnesses in the Gal lee raises questions about when in vestors can act on information that is not public. The case also signals a new zeal by regulators and law enforcement officials to clamp down on Wall Street crime after failing to detect the $68 billion Ponzi scheme run by Bernard L. Madoff.

At the center of this purported insider trading ring is Mr. Rajaratnam, who rose from a technology analyst to become a hedge fund billionaire.

Mr. Rajaratnam always remained close to his homeland, Sri Lanka, which was riven by fighting between its government and the Tamil Tigers, formally known as the Liberation Tigers of Tamil Eelam. The hedge fund manager rarely hesitated to reach into his wallet for causes related to the country. When the island was struck by a disastrous tsunami in 2004 - he had been there at the time, but was, inland he quickly organized a charity to raise money to rebuild homes.

In 2004, he also helped raise $120000 to buy dogs, to detect land mines littered throughout Sri Lanka.

Yet his giving was not without controversy. In 2005 and 2006, the charity he created, Tsunami Relief, gave $1.5 million to the Tamil Rehabilitation Organization, a group officially dedicated to helping victims of the fighting. But prosecutors have since charged the Tamil charity with aiding the rebel group, and its nonprofit status has been suspended.

A criminal complaint filed in Brooklyn federal court in 2007 described a wealthy supporter, identified only as "Individual B," who donated more than $2 million to the terrorist group in 2000 and 2004. People briefed on the matter confirmed a report by The Wall Street Journal that Individual B was Mr. Rajaratnarm, who was never charged or publicly identified in that case. Several defendants in that case have pleaded guilty to raising money for the Tigers.

A lawyer for Mr. Rajaratnam, James Walden of Gibson, Dunn & Crutcher, said in a statement that this client was not a Tiger supporter and that the money had been spent on "rebuilding thousands of homes for Tamils, Sinhalese and Muslims without discrimination."

Within the hedge fund industry, Mr. Rajaratnam was long known for his deep knowledge of and expansive contacts within the technology sector.

People close to the company describe the pressure within Galleon as intense with Mr. Rajaratnam demanding long hours and highly detailed research reports.

By the time he was arrested, Mr. Rajaratnam had cemented his position as a member of New York’s financial elite. Forbes estimated his net worth this year at $1.3 billion, earning him a spot on its list of richest people in the world. He donated more than $30,000 to Barack Obama Hillary Rodham Clinton and the Democratic Party in 2008.

And he sat on multiple charity boards, including that of the Harlem Children’s Zone, the American India Foundation and the Indian School of Business.

Mr. Rajaratnam built himself from the ground up: born in Sri Lanka, he was sent away for schooling, including at the University of Sussex and the Wharton School at the University of Pennsylvania. He became a technology analyst at the investment bank Needham & Company, rising through the ranks to become president. In 1992, he began a hedge fund for Needham clients, many of whom were technology executives themselves.

Mr. Rajaratnam left the firm in 1997, but took the fund and called it Galleon after the Spanish empire’s ships used to ferry gold and spices from the New World.

Several of Galleon’s employees had an engineering background like the firm’s founder. Many outside analysts envied the, extensive research reports their counterparts at Galleon produced, culled from regulatory filings, checkups on supply chains and sources within the companies they covered. At its peak, the firm managed $7 billion in assets, but that figure has since fallen to about $3.7 billion.

The firm also made no secret that among its investors included technology executives. Among them was Anil Kumar, a McKinsey director who did consulting work for Advanced Micro Devices. Another defendant, Rajiv Goel, is an Intel executive who is accused of leaking information about the chip maker’s earnings and an investment in Clearwire.

Prosecutors also say that a Galleon executive on the board of People Support, an outsourcing company, regularly tipped off Mr. Rajaratnam about merger negotiations with a subsidiary of Essar Group of India.

Galleon has previously been accused of wrong doing by regulators. In 2005, it paid more than $2 million to settle an S.E.C. lawsuit claiming it had conducted an illegal form of short-selling.