During Monday’s summit between President Donald Trump and Russian President Vladmir Putin plenty of news was made, but one man in particular was singled out during the one-on-one between the two heads of state — American-born financier Bill Browder.

Browder has been a thorn in the side of Putin and his administration for over a decade, as the London-based financier has made it his mission to spread awareness about the growing threat of Russian corruption and influence on Western democracy by sharing his personal experiences with the Russian government. Browder has said he is Putin’s No. 1 foreign enemy.

Who is Bill Browder?

William F. Browder, 54, founder and CEO of Hermitage Capital Management, an investment firm based in London, is a fund manager who was one of the largest foreign investors in Russia until 2005 when he was banned from entering the country. Since then, he has become a vocal critic and activist, working to sound the alarm across Europe and the U.S about Russia’s deceptive and malignant political strategies.

In a recent essay for TIME, Browder called out Putin directly, arguing that he is a liar who values money over human life and often bluffs when it comes to making deals with foreign powers. Browder accused Putin of orchestrating the murders of those who oppose him, and interfering in multiple foreign democratic elections, from the U.S., U.K., France, Italy and Germany. Browder also warned that Putin is capable of “planning targeted assassinations of dissidents and business competitors with his secret police” and that negotiating with him is useless because the former KBG agent sees compromise as a weakness. He says Putin should never be believed: “Whatever he tells you, it’s not true.”

The fight against Russia is extremely personal for Browder. He also detailed how his lawyer, Sergei Magnitsky, died suspiciously in a Russian prison in 2009 after helping to expose Kremlin fraud when he “uncovered a massive Russian government corruption scheme.” Browder helped pass the Global Magnitsky Human Rights Accountability Act in 2012, which authorized the U.S. president to sanction people violating internationally recognized human rights in Russia, among other punishments.

What is his connection to the 2016 U.S. presidential election?

On Monday, Putin suggested that he would allow Special Counsel Robert Mueller to interrogate the 12 Russians indicted for meddling in the 2016 U.S. presidential election if Russian authorities could also interview persons who may have been involved in illegal dealing in Russia. He was talking about Browder. Putin accused him of evading taxes and illegal giving hundreds of millions of dollars to Hillary Clinton’s campaign. (There is no public evidence to back up Putin’s claim.)

Monday was not not the first time Browder’s name has come up during talk of election meddling. His name was mentioned at the now-infamous Trump tower meeting in June 2016, during which Trump campaign officials, including Donald Trump, Jr., met with a Russian lawyer who told the campaign it had damaging information about Hillary Clinton.

Browder, who is reportedly worth some $100 million, has also authored the New York Times best-seller “Red Notice: A True Story of High Finance, Murder and One Man’s Fight For Justice,” about his time investing in the Russian stock market and the corruption he says he encountered.

Harvard Business School has used Browder’s business experiences with Russia as a case study, which Browder has called “the textbook example of the cost of corruption in emerging markets.”

What did Putin say about him?

Here’s Putin’s remarks from a joint press conference, which came after he spoke about allowing the U.S. to interview Russians accused of interfering with the election, arguing that the U.S. should allow Russia to do the same:

But in this case, there is a — there’s another condition. This kind of effort should be a mutual one. Then we would expect that the Americans would reciprocate, and that they would question officials, including the officers of law enforcement and intelligence service of the United States, whom we believe are — who have something to do with illegal actions on the territory of Russia, and we have to — to request the presence of our law enforcement. For instance, we can bring up the Mr. Browder in this particular case. Business associates of Mr. Browder have earned over $1.5 billion in Russia. They never paid any taxes, neither in Russia nor in the United States, and yet the money escaped the country. They were transferred to the United States. They sent huge amount of money, $400 million as a contribution to the campaign of Hillary Clinton. Well, that’s the personal case. It might have been legal, the contribution itself, but the way the money was earned was illegal.

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