Maria Butina, the Russian woman charged in US federal court last week with acting as an unregistered agent of her Government, received financial support from Konstantin Nikolaev, a Russian billionaire.
Nikolaev has investments in US energy and technology companies, according to a person familiar with testimony she gave Senate investigators.
Butina told the Senate Intelligence Committee in April that Nikolaev provided funding for a gun rights group she represented, according to the person.
A spokesman for Nikolaev confirmed that he was in contact with her as she was launching the pro-gun rights group in Russia between 2012 and 2014. He declined to confirm whether Nikolaev gave her financial support.
Nikolaev's fortune has been built largely through port and railroad investments in Russia. He also sits on the board of American Ethane, a Houston ethane company that was showcased by US President Donald Trump at an event in China last year, and is an investor in a Silicon Valley start-up.
Nikolaev has never met Trump, according to his spokesman.
However, Nikolaev's son Andrey, who is studying in the United States, volunteered in the 2016 campaign in support of Trump's candidacy, according a person familiar with his activities.
Konstantin Nikolaev was spotted at the Trump International Hotel in Washington, DC, during Trump's inauguration in January 2017, according to two people familiar with his presence.
In a court filing last week, prosecutors said Butina's emails and chat logs are full of references to a billionaire as the "funder" of her activities. They wrote that the billionaire is a "known Russian businessman with deep ties to the Russian Presidential Administration."
Prosecutors did not identify Butina's funder by name but said he travels often to the United States and was listed by Forbes this year as having a net worth of US$1.2 billion - which is the same as Nikolaev's current listing.
Butina was ordered held in custody this week after she was charged with conspiring to work as a Russian agent.
Prosecutors allege that she sought to meet GOP politicians and infiltrate conservative organisations, including the National Rifle Association, at the direction of a Russian government official, in an attempt to advance the Kremlin's interests.
According to prosecutors, for two years, she travelled back and forth to the US, often accompanying Russian central banker Alexander Torshin to NRA events and other political meetings. Prosecutors have said that her activities were directed by a high-level Russian government official who matches the description of Torshin.
In August 2016, she came to Washington to study full-time as a graduate student at American University.
Butina's lawyer, Robert Driscoll, has said she is not a Russian agent but rather a student interested in learning about the American political system.
The Russian Government has proclaimed Butina's innocence, promoting the hashtag #freeMariaButina on social media. Russian Foreign Minister Sergei Lavrov pressed Butina's case with Secretary of State Mike Pompeo in a phone call, according to a statement by the Russian Government.
Driscoll declined to comment on Nikolaev, but said that the Russian businessman cited by prosecutors was a financial supporter of the gun-rights group Butina founded in Russia, the Right to Bear Arms. She met him in person only twice, he said.
Prosecutors cited Butina's interactions with the Russian billionaire to argue she should not be allowed out of jail while awaiting trial. They argued that she has "ties to the Russian oligarchy" and knows wealthy men who could be in a position to offer her "safe harbour" if she decided to flee the US.
Nikolaev last had contact with the Russian activist in 2014, according to his spokesman, who said that at the time, Butina had a "public profile in Russia as a blogger on key domestic issues that were of interest."
Nikolaev's connections to the Russian Government "cannot be characterised as deep," his spokesman said.