Felix Sater, the Russian-born, Brooklyn-raised developer, and Donald Trump have known each other for many years. Sater’s company Bayrock Group LLC was located inside Trump Tower and Sater even had Trump Organization business cards listing him as a ‘senior advisor to Donald Trump.’

When their business relationship began in 2003, Sater was instrumental in finding funding for Trump’s SoHo building—funding from wealthy foreigners, with a key focus on Russians. In July, it was reported that Felix Sater is cooperating with Robert Mueller's investigation:

The Financial Times reported Thursday morning that Felix Sater, former business partner of President Donald Trump with deep ties to the Mafia and Russian government, is cooperating in an international investigation into an alleged money-laundering network. Sater has a history of channeling money from prominent families in the Eastern bloc into Trump properties. This could pose problems for Trump, given Sater’s history of outing former close associates in exchange for immunity.

According to recent reports from The New York Times and Bloomberg, these financial connections are also being investigated by special counsel Robert Mueller as part of the investigation into the Trump campaign’s possible collusion with Russia.

Sater is undoubtedly one of the more unsavory people the president has conducted business with. He was famously involved in a clash at a bar where he stabbed another man in the face with the stem of a martini glass, an assault that landed him in prison for a year. He pleaded guilty to racketeering as part of a $40 million stock fraud scheme orchestrated by the Mafia but avoided jail time by becoming a valuable federal informant for the FBI and CIA. Andrew Weissmann, the prosecutor who negotiated that plea deal, has been hired by Robert Mueller.

Sater first began pitching the Trump Tower Moscow project in 2005. Even after a spate of lawsuits and Sater being forced to part ways with Bayrock after his criminal history was revealed, his connections with Trump apparently never crumbled. In late 2015, Felix Sater was again pitching a Trump Tower Moscow project to Donald Trump, via his personal attorney Michael Cohen. Sater believed the Russian deal would help Donald Trump win the presidency:

A business associate of President Trump promised in 2015 to engineer a real estate deal with the aid of the president of Russia, Vladimir V. Putin, that he said would help Mr. Trump win the presidency.

The business associate, Felix Sater, wrote a series of emails to Mr. Trump’s lawyer, Michael Cohen, in which he boasted about his ties to Mr. Putin and predicted that building a Trump Tower in Moscow would be a political boon to Mr. Trump’s candidacy.

“Our boy can become president of the USA and we can engineer it,” Mr. Sater wrote in an email. “I will get all of Putins team to buy in on this, I will manage this process.”

“Our boy”? Sounds like the two had a pretty good relationship over the course of nearly 15 years, no? Well, watch what happened in a 2013 interview when British investigative journalist John Sweeney asked Trump about his association with Felix Sater, despite his known past as a criminal and his ties to the Russian mafia. This may be the only time you ever see Donald Trump running from a camera: