Antonio Olmos for The New York Times

William Browder in his London office. He said he had learned that his former holding companies had been used to embezzle $230 million from the Russian treasury.

William Browder was one of the most prominent foreign investors in Russia, a corporate provocateur who brought the tactics of Wall Street shareholder activists to the free-for-all of post-Soviet capitalism. Until, that is, the Kremlin expelled him in 2005.

Browder then focused on protecting his billions of dollars of stakes in major Kremlin-controlled companies like Gazprom, and fighting to return to a land where he had deep and unusual family ties. So when he ran into Dmitri Medvedev, the country's future president, at the Davos economic forum last year, Browder saw his chance.

During a brief conversation at a dinner at the Swiss resort, he pressed Medvedev for assistance in regaining his Russian visa. Medvedev, at the time a top aide to then-President Vladimir Putin, agreed to pass along his request.

A short time later, Browder's office received an unexpected telephone call from a senior Moscow police official, who said he had learned of Browder's new visa application and might be able to help.

"My answer will depend on how you behave, what you provide, and so on," the official said, according to a recording of the call supplied by Browder. "The sooner we meet and you provide what is necessary, the sooner your problems will disappear."

Browder's problems, in fact, were just beginning.

The phone call was one move in a wide-ranging offensive by Russian law enforcement that exposed Browder to the kind of crippling investigations that Kremlin critics have regularly endured under Putin. It appeared that the ultimate goal was not only to seize Browder's investment empire, but also to make him an example of what happened to those who did not toe the government's line.

His downfall offers a study in how the Kremlin wields power in the Putin era: The rule of law is subject to its wishes, and those out of favor are easy prey.

Browder fell victim to the official corruption afflicting Russia, and the Kremlin's unwillingness to combat it by bolstering the independence of the police and courts. The Kremlin may be reluctant to do so because it wants wealth in Russia to accrue to those loyal to the leadership.

Until his visa was canceled and he moved his operations to London, Browder cut a colorful figure in Russia, a foreign version of the Russian oligarchs who earned their fortunes in the mass privatization after the fall of the Soviet Union.

He courted publicity, and his background made a good story: he is the grandson of Earl Browder, the leader of the American Communist Party for much of the 1930s. He often said that, not unlike Russia itself, he rebelled by becoming a capitalist.

He arrived in Russia in 1996 after a stint in London as an investment banker, and quickly saw opportunities. The Russian economy was undergoing colossal changes, and Browder positioned his company, Hermitage Capital, as a vehicle for Western investors to get a piece of the action.

After Putin became president in 2000, Browder became a vocal supporter of the Kremlin, saying that Russia needed an authoritarian leader to establish order and calling Putin his "biggest ally" in the effort by Hermitage to reform big business. Browder thrived, and the funds managed by Hermitage grew to more than $4 billion.

Browder does not know exactly why the Kremlin turned against him. But the Kremlin was consolidating control over prized companies like Gazprom and appeared to be chafing at criticism from outside shareholders.

Once things went bad, Browder had no recourse. Police confiscated vital documents from the office of his lawyer in Moscow. He discovered that his holding companies had been stolen from him and re-registered in the name of a convicted murderer in a provincial city.

Whoever was behind the scheme succeeded in taking over much of Browder's corporate structure in Russia, but failed to get at his investors' money. Even so, in recent weeks, Browder said he had learned that his former holding companies had been used to embezzle $230 million from the Russian treasury.

This article is based on interviews with Browder, his associates and lawyers, as well as on numerous documents they provided that they say prove corruption. Many of his assertions were confirmed independently.Requests for comment were made to several law-enforcement agencies in Russia that Browder accuses of carrying out or refusing to investigate the scheme. They did not respond or said they would not comment.

The Kremlin has not spoken publicly about his case, despite frequent appeals by Browder and senior British and U.S. officials. Twice in the past two years, Putin has been asked by reporters about Browder. Both times, he denied even knowing Browder's name.

"I don't know who this Browder is, as you say, why he cannot return to Russia," Putin, who is now prime minister, said in May.

"Russia is a big country," Putin said. "There might have been some kind of complications. There might have been some kind of conflicts - conflicts with the authorities, conflicts in the business world, interpersonal conflicts. But that's life, it's complicated and varied. If a person thinks that his rights have been violated, let him go to court. We have a legal system that works, thank God."

A spokesman for Medvedev, who succeeded Putin as president in May, confirmed that Medvedev had spoken with Browder at Davos last year, but would not comment further.

Medvedev, a former law professor, has vowed to wage war on corruption. He often says that Russia is plagued by "legal nihilism." Still, the Kremlin under Medvedev has also snubbed Browder.

"If ever there was a definition of legal nihilism, this is it," Browder said during an interview in his office in London, where he now lives.

"I was actually fighting to make Russia a better place, and fighting against corruption, which is something that they should have given me a medal for," Browder said. "Instead, they drive me out of the country and tarnish everything that I did there."

For Browder, who is 44, Russia was more than a place to do business, His grandfather, Earl Browder, was a Communist from Kansas who moved to the Soviet Union in 1927, staying for several years and marrying a Russian. Earl Browder returned with her to the United States to lead the Communist Party for a time, even running for president.

William Browder also aspired to help build Russia. He hoped to get rich, but he also argued that his fight against corporate malfeasance would benefit the country. After all, even as oligarchs got absurdly wealthy in the 1990s in highly questionable methods, many Russians fell into poverty.

"I had a lot of my family in me, and tried to find a way of connecting my past to my future," he said.

Browder grew up in Chicago and attended the University of Chicago. After graduating from Stanford Business School in 1989, he set off for London. He later became a British citizen, not out of antipathy toward the United States, he said, but because he felt comfortable there.

Hermitage Capital was first bankrolled by Edmond Safra, the billionaire founder of Republic National Bank in New York. Browder said that the late Safra taught him not to shy from kicking up a scandal to protect his interests.

Following that advice, Browder made a lot of money and a lot of enemies in Russia, garnering a reputation as a sharp-eyed analyst of Russian industry who could also be abrasive and headstrong.

Hermitage started with $25 million from Republic. The fund was so profitable in its first 18 months, reaping a gain of 850 percent, that it soon attracted more than $1 billion from institutional investors and others in the West. In the Russian financial collapse of 1998, it plunged to $125 million, but it recovered during the past decade, reaching a peak of more than $4 billion.

Despite his success, Browder led a relatively austere lifestyle in Moscow, eschewing the trappings of many expatriates and working so hard, he says, that he learned to speak barely a word of Russian. He tried to keep a low profile, but did employ bodyguards when he engaged in shareholder battles.

Browder focused his investments on the largest Russian companies, most of them in the energy sector and under some Kremlin control. Hermitage became expert at conducting forensic audits into their finances, uncovering all manner of wrongdoing, from insider trading to outright theft. He often leaked the information to the Russian and international press.

"It became a matter of desperation, not inspiration," he said. "You had to become a shareholder activist if you didn't want everything stolen from you."

Gazprom, one of the world's largest companies, was a favorite target. Browder discovered that billions of dollars in natural gas had been sold at deeply discounted prices to shady intermediaries.

But by 2005, Putin had assumed complete control over Gazprom as part of his drive to re-nationalize crucial energy assets. When Hermitage released a dossier assailing mismanagement and corruption at the company, the Kremlin had had enough.

A few months later, Browder's visa was canceled. Over the next two years, several of Browder's associates and lawyers, as well as their relatives, were victims of crimes, including severe beatings and robberies during which documents were taken. None was solved.

The real trouble, though, got under way in June 2007, with Browder stuck outside the country.

Dozens of police officers swooped down on the Moscow offices of Hermitage and its law firm, confiscating documents and computers. When a member of the firm protested that the search was illegal, he was beaten by officers and hospitalized for two weeks, said the head of the firm, Jamison Firestone.

Supervising the raids was the same police official who had called Browder's office about the visa three months earlier, Lieutenant Colonel Artem Kuznetsov of the Department of Tax Crime of the Interior Ministry. He said he was seeking evidence in an inquiry into whether one of Hermitage's related entities, called Kameya, had underpaid its taxes by $44 million.

According to court documents obtained by Hermitage lawyers, the FSB, successor to the KGB, approved the inquiry. The Interior Ministry and the FSB would not comment.

Their role against Hermitage was not unusual. During Putin's tenure, law enforcement has been repeatedly deployed against Kremlin critics or those whom the Kremlin did not favor in business disputes. Opposition parties faced numerous investigations during the parliamentary elections last autumn.

In recent months, TNK-BP, a large Russian oil company, has been subjected to 14 such inquiries, apparently in an effort to push out BP, the British oil giant, which owns half the venture, BP said. Analysts say the Kremlin wants a state company to take over TNK-BP.

The issues surrounding the Hermitage tax payment were complex, but there was a larger question: Why did the police need to carry out searches and seize so many documents, including many unrelated to Kameya, when such tax disputes are first supposed to be handled through routine bureaucratic channels? Even more curiously, Hermitage asked the Russian tax authorities whether Kameya owed back taxes. The answer was no.

But it did not matter. Hermitage was about to become victim of what is known in Russia as corporate raiding, which involves seizing companies and other assets with the aid of corrupt law enforcement and judges. The phenomenon has flourished under Putin.

In the weeks after the police seized the corporate documents, someone used them to transfer the ownership of three of Hermitage's holding companies to an entity based in Kazan, a provincial capital 450 miles east of Moscow. The registered owner of the entity was a man with a murder conviction, records show.

Now that the corporate raiders had seized the three Hermitage holding companies, they resorted to a classic strategy to try to drain them of money.

A lawsuit was filed in a court in St. Petersburg in July 2007 against the holding companies, asserting that they had defrauded another company, Logos Plus, of hundreds of millions of dollars in a 2005 deal involving Gazprom stock.

In fact, everything about the lawsuit was bogus, Hermitage lawyers said.

Hermitage had never done business with Logos Plus. The documents submitted to the court had obvious inconsistencies, suggesting that conspirators were not worried about being caught. A power of attorney for one of the Hermitage companies was dated four months before the company had been created.

While it is unclear whether the judge knew about the fraud, she let the case go forward anyway. Lawyers whom Browder had never heard of showed up to defend the Hermitage companies and admitted wrongdoing. The judge ruled in favor of Logos Plus.

In all, 15 such claims were put forth in similar cases, and judges issued a total of $1.26 billion in judgments against Hermitage. Hermitage did not even learn of the cases until three months later.

In the end, the raiders got nothing from Hermitage.

After his visa was canceled, concerned about such an onslaught, Browder had quietly moved his Russian assets off shore and sold most of them. The holding companies were shells.

Still, the plot was not finished. In recent weeks, Hermitage discovered that the fake lawsuits had served another purpose. The raiders used the legal judgments to alter the holding companies' balance sheets, wiping away their profits for 2006.

The raiders then went to the tax authorities and applied for a refund on taxes that Hermitage had paid in 2006 on the profits. The authorities handed them $230 million from the Russian treasury, Hermitage lawyers said.

While Browder did not suffer grievous financial losses, his work in Russia has been ruined. He has only small investments left in the country, and has evacuated his Russian staffers to London, fearing for their safety.

Browder has, during the past year or two, reinvented himself: Hermitage now has more than $3 billion invested in other parts of the world.

Beginning in December, Hermitage and its bankers filed dozens of lengthy complaints with Russian government agencies, presenting numerous pieces of evidence, including the phone call from Kuznetsov. To no avail.

Medvedev appointed a committee in May to develop an anti-corruption program, and Hermitage sent letters to its members. None responded.

At the same time, as Browder has stepped up his complaints, the Interior Ministry has set its sights on him personally. It has opened a criminal inquiry into whether or not he violated an obscure tax law in 2001.

Hermitage did persuade one agency, the State Investigative Committee, which is part of the prosecutor's office, to examine the case. But Hermitage has come to realize that this inquiry will also most likely go nowhere.

Last month, a Hermitage lawyer went to a meeting at the committee about the case and saw a familiar face. One of the officials helping to lead the inquiry into the Hermitage allegations is Lieutenant Colonel Kuznetsov.