A tombstone on the grave of lawyer Sergei Magnitsky, who died in jail, at a cemetery in Moscow on Nov. 16, 2012. (Misha Japaridze/AP)

Three years after his death, a soft-spoken Russian tax adviser has become a powerful presence in world affairs, roiling relations between his country and the West, especially the United States.

Sergei Magnitsky’s name was virtually unknown in Washington when he died in November 2009. This past week, the U.S. Senate overwhelmingly passed a law in his honor, the Sergei Magnitsky Rule of Law Accountability Act. The law serves as a reprimand to Russia over its human rights record, imposing penalties on abusers.

By the time the Senate voted Thursday — the House had given its enthusiastic approval in November — the 37-year-old Magnitsky had come to represent the intense conflict between Russia and the West over democracy and the rule of law.

Magnitsky’s story has been told in Washington, repeatedly, by William F. Browder, founder and chief executive of Britain-based Hermitage Capital Management, once the largest foreign investor in Russia. At first, he had trouble getting people to listen to the tangled, hard-to-believe details, but he kept telling it.

Browder worked as diligently to make Magnitsky’s name known in the West as he had done in earning a fortune in Russia. The American-born money manager made millions for his clients by investing in undervalued companies and then becoming an activist shareholder, improving company management — and value. Even today, many Russians think there is something wrong with making money that way.

A handout photo provided by Hermitage Capital Management taken on Sept.17, 2007, shows Russian lawyer Sergei Magnitsky smiling in Moscow. (-/AFP/GETTY IMAGES)

Browder, who had initially admired Russian President Vladimir Putin’s strong hand, suddenly found himself barred from the country in 2005 when he returned from a trip abroad and was denied entry, despite his valid visa. He never got an explanation, although he had been tangling with Gazprom, the gas giant with close ties to Putin.

Browder moved his assets out of the country and began operating his company from London. Back in Moscow, Magnitsky was working for the U.S.-owned law firm Firestone Duncan, advising Hermitage Capital on tax matters. The young lawyer eventually uncovered a plot, already being carried out by tax and police officials, to steal $230 million from the Russian treasury by filing a fraudulent return for income taxes Hermitage had paid in 2006. The return used documents stolen from Hermitage companies to establish losses that would justify a huge refund, according to Senate testimony.

Magnitsky was arrested in November 2008 after turning over evidence of the fraud to police. At first, he was charged with helping Hermitage find ways to underpay taxes a few years earlier. Later, he was accused of masterminding the $230 million theft.

Finally, in June 2009, Browder was able to testify before the U.S. Helsinki Commission, co-chaired by Sen. Benjamin L. Cardin (D-Md.), which was examining human rights in Russia under the title, “The Medvedev Thaw: Is it Real? Will it Last?”

Magnitsky was still alive that day, lingering in pretrial detention. He died in jail the following November. The official cause was variously given as a heart attack or pancreatic disease. Independent investigators found evidence of torture and beatings.

Magnitsky’s death launched Browder on a mission to ensure punishment for those who had harmed him and galvanized Cardin and other U.S. politicians — including Sens. John McCain (R-Ariz.) and Joseph I. Lieberman (I-Conn.) — into action. On the Senate floor this week, Cardin recalled the impression that the plight of Soviet Jews had made on him years ago as they fought an earlier battle for human rights. In 1987, he joined a march on Washington in their support. He wore wristbands bearing the names of refuseniks, those once refused permission to emigrate by Soviet authorities.

The result of Browder’s effort and Cardin’s response was the Magnitsky law, imposing U.S. visa and financial sanctions on officials connected to Magnitsky’s death. Canada and Europe are considering similar laws.

By Friday, the Magnitsky affair had grown into a major diplomatic issue. Russian Foreign Minister Sergei Lavrov said he had told Secretary of State Hillary Rodham Clinton in Dublin that Americans guilty of human rights violations will be barred from Russia. Meanwhile, other Russian officials issued a report criticizing Europe for human rights violations, and the Foreign Ministry also released a strong statement condemning the United States.

“It is strange and savage to hear human rights claims from politicians of the state that officially legalized torture and kidnappings all over the world in the 21st century,” the statement said, apparently referring to the U.S. practice of sending terrorism suspects to third countries for interrogation and to the U.S. military prison in Guantanamo Bay, Cuba.