Who is Bill Browder?

Businessman Bill Browder is expected to testify on Wednesday before the Senate Judiciary Committee in the Russian investigation into U.S. election meddling.

Browder, who is the CEO of Hermitage Capital Management, was previously a hedge fund manager in Russia and one of the country's most successful foreign investors.

The businessman also worked on reducing corporate corruption in the country for years. But in 2005, his entry into Russia was revoked after the government declared him a "threat to national security," according to his website.

In 2012, he spearheaded the Magnitsky Act -- a sanctions package on Russia that was imposed for the first time in 35 years. The sanctions were created to punish Russian officials involved in the death of Browder's accountant, Sergey Magnitsky, who was jailed in 2008 and died under mysterious circumstances a year later.

Magnitsky uncovered a $230 million corruption scheme involving Russian officials just before he was arrested.

Browder also is familiar with Russian lawyer Natalia Veselnitskaya, who recently came into the spotlight when it was revealed she met with Donald Trump Jr. last year during the U.S. election, reportedly to offer damaging information on Democratic presidential candidate Hillary Clinton. Browder told NPR Veselnitskaya was part of the campaign to repeal the Magnitsky Act.

On Wednesday, Browder is expected to testify about Russian foreign agents working in the U.S. and Russia's attempt to repeal the Magnitsky Act. Browder said in his prepared opening statement ahead of his testimony that he will be speaking about "the enablers who conducted this campaign in violation of the Foreign Agents Registration Act, by not disclosing their roles as agents for foreign interests."