A longtime Trump business associate who was born in Moscow and served time for stabbing a man in the face with a broken margarita glass could hold the key to Robert Mueller's Russia investigation.

Felix Sater, 52, was identified as "Individual 2" in the special counsel’s "criminal information" document filed in the case against former Trump lawyer Michael Cohen, who pleaded guilty Thursday to lying to Congress. President Trump himself was "Individual 1."

Sater was born in Russia to Jewish parents and the family emigrated to Israel and then moved to Baltimore and finally New York, when he was eight. He spent a decade as an FBI informant and once boasted: "I was building Trump Towers by day and hunting Bin Laden by night."

A childhood friend of Cohen, he was a successful Wall Street broker at 24, was jailed for a year at 27 prison after a brutal bar fight and at 32 he was accused of conspiring with the Mafia to launder money and defraud investors.

Court transcripts show Sater got into an argument with a commodities broker at a bar in 1991. Sater grabbed a large margarita glass, smashed it on the bar and plunged the stem into the right side of the broker’s face. The victim suffered nerve damage and 110 stitches to his face. “I got into a bar fight over a girl neither he nor I knew,” Sater said in a 2007 interview. “My life spiraled out of control.”

A federal complaint brought against him in a 1998 money laundering and stock manipulation case was filed in secret and remains under seal. Two years later, he was named as an “unindicted co-conspirator” and key figure in a $40 million scheme involving 19 stockbrokers and organized crime figures from four Mafia families

Sater - who often spells his name "Satter" to distance himself from his past - met Trump in 2003 when he was managing director of Bayrock Group LLC, a real estate development company firm, court records show. The company was based in Trump Tower and the future president was looking to expand his business and branding organization around the globe.

Although few projects were built, Sater worked on hotel and condominium deals with the Trump Organization through 2010 in New York, Florida, Arizona, London, Moscow and elsewhere even as he secretly helped the FBI infiltrate and take down organized crime figures. He played a major role in the development of the Trump SoHo project, completed in 2010. Trump has denied they were close, but Sater had access to Trump's inner circle as recently as this year.

“If he were sitting in the room right now, I really wouldn't know what he looked like,” Trump testified in a video deposition for a civil lawsuit in 2013. During the 2016 presidential campaign he responded to a question about why he hired the convicted felon and government informant by saying: "Felix Sater, boy, I have to even think about it. I’m not that familiar with him."

In Thursday's plea document, Cohen admitted lying about trying to strike a deal over a Trump Tower in Moscow as late as June 2016. He stated: “'I primarily communicated with the Moscow-based development company ... through a U.S. citizen third-party intermediary, [Individual 2],'"quoting a letter written by Cohen to congressional lawmakers about a project to build a Trump Tower in Russia.

In the August 2017 letter, he wrote: "I primarily communicated with the Moscow-based development company ... through a U.S. citizen third-party intermediary, Mr. Felix Sater."

Cohen was charged with lying to Congress about his efforts to get Trump Tower-Moscow built by Mueller. He took a plea deal Thursday. One of those lies was Cohen claiming he and the Trump Organization had abandoned the project in January 2016.

According to the court filing, Cohen and Sater were still talking about getting approval from the Russian government for the project “as late as approximately June 2016.”

The court filing also reveals that Sater asked Cohen on May 4, 2016, when then-candidate Donald Trump could come to Russia.

Cohen responded that Trump would do so “once he becomes the nominee after the convention.” The next day, according to the court filing, Sater invited Cohen to travel to St. Petersburg in June to attend a forum as a guest of Russian President Vladmir Putin’s spokesman. Cohen agreed to go, but the trip never came to fruition.

According to the statement Cohen gave the House and Senate Intelligence committees about the proposed Trump Tower-Moscow, it was Sater who first suggested in mid-January 2016 that he email Dmitry Peskov, Putin's spokesperson, about the project.

On Nov. 3, 2015, Sater told Cohen in an email that he had arranged for Ivanka Trump to sit in Putin’s private chair in the Kremlin. “I will get Putin on this program and we will get Donald elected,” he wrote. “Our boy can become president of the USA and we can engineer it.”

It is unclear if Sater has been interviewed by Mueller's prosecutors.