Every time someone asks Donald Trump if he knows Felix Sater, his Russian-born, Brooklyn-bred former business associate, Trump draws a blank. Despite the fact that Sater worked on and off for a decade with the Trump Organization, and despite his recent headline-making appearance as an exuberant negotiator on behalf of Trump’s hardnosed attorney, Michael Cohen, in seeking to build a “massive Trump Tower in Moscow” last year, Trump ducks.

“I mean, I’ve seen him a couple of times; I have met him,” Trump said, in a deposition in a court case involving Sater in 2013. And The New York Times reported him as saying, “If he were sitting in the room right now, I really wouldn’t know what he looked like.” As late as 2015, when asked about Sater, Trump hemmed and hawed. “Boy, I have to even think about it.”

It’s no wonder that Trump, especially now that he’s under investigation over his ties to Russia and its meddling in the 2016 election, would respond to questions about Sater by saying: Who’s he?

Of all the characters caught up in Russiagate, none come close to Sater for having a decades-long record as a larger-than-life, outside-the-law, spy agency-linked wheeler-dealer from the pages of a John le Carré novel. His past record includes a conviction for lacerating a man’s face with a broken margarita glass in a bar brawl and his involvement in a multimillion-dollar stock fraud and money-laundering scheme. Despite that record, which came before he worked with Trump, Sater spent nearly a decade working with the Trump Organization in search of deals in Russia and other former Soviet republics. But on August 28, Sater made the front pages of the Times and The Washington Post, thanks to leaked copies of e-mails that he sent in late 2015 and early 2016 to Cohen, concerning Sater’s efforts to work with a group of Russian investors to set up a flagship Trump property in the Russian capital.

In language that Cohen himself described to the Times as “colorful,” Sater seemed nearly beside himself as he reported on his work in Moscow on behalf of Trump:

“Our boy can become president of the USA and we can engineer it,” wrote Sater. “I will get all of [Vladimir] Putins [sic] team to buy in on this, I will manage this process.… I will get Putin on this program and we will get Donald elected.” Echoing a line that would later become Trump’s own description of why he and Putin might get along, Sater wrote that the Russian leader “only wants to deal with a pragmatic leader, and a successful business man is a good candidate for someone who knows how to deal.”

Sater couldn’t resist adding, “Michael I arranged for Ivanka to sit in Putins [sic] private chair at his desk and office in the Kremlin.” According to the Times, Sater was “eager to show video clips to his Russian contacts of instances of Mr. Trump speaking glowingly about Russia.” Which, of course, Trump has done repeatedly over the years. And, though Trump has denied that he has any business interests in Russia, even as he was gearing up for the Republican presidential primary race, Cohen and Sater were deep into previously undisclosed talks with Russian partners about constructing a Trump-branded hotel, according to The Washington Post. In a statement to the House Permanent Select Committee on Intelligence last week, Cohen did admit writing to Dmitry Peskov in connection with Sater’s work. Peskov, a spokesman for Vladimir Putin, confirmed the contact.

So who, exactly, is Felix Sater? Tim O’Brien, author of a biography of Trump, wrote about Sater in an article titled “Lean, Mean Trump-Russia Machine.” He was born in 1966 in the Soviet Union, and he and his family moved to Brighton Beach in Brooklyn, New York, when he was just 8. According to a recent Guardian profile, Sater’s relationship with Cohen—and to organized crime—goes way back:

Sater’s links to Trump’s circle can be traced back to not long after he came to the US as a child. His father, Mikhail Sheferovsky (who changed the family name after arriving in New York) became a local crime boss in Brighton Beach and Sater grew up on that side of Brooklyn, where he got to know another teenager in the neighbourhood, Michael Cohen, a Long Island boy who would go on to become Trump’s personal lawyer and vice-president of the Trump Organization.

Sorting out Sater’s checkered past leads into a convoluted labyrinth of crime, legal entanglements, shady deals, alleged ties to US and foreign intelligence agencies and, of course, intimate connections to Donald Trump and the Trump Organization. The best comprehensive account of Sater’s long and complicated path was written by Andrew Rice and published in August in New York magazine under the headline “The Original Russia Connection.” Rice’s account, which includes parts of a lengthy interview with Sater, draws heavily on a 2007 breakthrough piece by Charles Bagli in The New York Times. Bagli was the first to uncover and report in depth on Sater’s criminal past. This past February the Times published a blockbuster story by Megan Twohey and Scott Shane recounting an effort by Sater, Cohen, Gen. Mike Flynn, and a Ukrainian politician to put forward a half-cocked Ukrainian “peace plan” and deliver it, freelance fashion, to the White House. In addition, various lawsuits, testimony, and depositions by the characters in Sater’s erratic orbit, including by Trump himself, provide valuable material in figuring out who Sater is and what role he plays in the Trump-Russia story. In this piece, I draw on all of these sources and more.

Sater’s first run-in with the law came in 1991—according to the indictment, as reported by Bagli in the Times—when Sater, then an upstart stockbroker in his mid-20s, “grabbed a large margarita glass, smashed it on the bar and plunged the stem into the right side of [a rival] broker’s face. The man suffered nerve damage and required 110 stitches to close the laceration on his face.”

Sater, who served time in prison for that assault, was barred from financial trading by the National Association of Securities Dealers. Yet in 1993, Sater and several partners took over a securities firm called White Rock Partners, later called State Street Capital Markets, which portrayed itself as a legitimate brokerage firm but, in fact, ran a criminal enterprise involving stock fraud, money laundering, and a so-called “pump and dump” scheme that involved conspiring to inflate the apparent value of near-worthless stocks, sell them off to unsuspecting investors, and cash in. In so doing, for protection Sater drew on the assistance of his father’s friends in the Genovese crime family. According to Rice’s New York piece, Sater “laundered fraud proceeds through a labyrinthine network of Caribbean shell companies, Israeli and Swiss bank accounts, and contacts in New York’s Diamond District.” In the mid-1990s, New York reports, Sater spent a great deal of time in Moscow, where, according to a friend and business partner, Sal Lauria—who later wrote a book about all of this—“We were dealing with ex-KGB generals and with the elite of Russian society.”

It all came crashing down in 1998, when New York City police uncovered a stash of guns and documents in a mini-storage locker in SoHo implicating Sater and his partners in the fraud and money-laundering schemes. According to the Times, citing other defendants in the case, Sater pled guilty to racketeering charges for bilking at least $40 million from his investors. Using Sater’s testimony, the feds eventually convicted 19 of Sater’s cronies, including half a dozen who had mob connections. Significantly, the prosecutor who oversaw Sater’s cooperation agreement in the 1998 indictment, now sealed, was Andrew Weissmann—who is currently one of 16 prosecutors and criminal justice officials on the staff of special counsel Robert Mueller, who’s leading the Russiagate inquiry.

Enter the spies. During his time in Moscow and traveling around eastern Europe, Sater began cultivating ties to arms dealers, officials in US law enforcement and national security agencies, and—according to his interview in New York—even meeting with the GRU, the Russian military intelligence agency. In order to get some bargaining power after he was indicted in 1998, according to Sater himself, he told the FBI that he had obtained valuable information about Osama bin Laden, a cache of Stinger missiles, and more. His information, it seems didn’t pan out—but after 9/11, Sater did cooperate in some fashion with the US government. Overseeing the Sater case back then was none other than Loretta Lynch, then US Attorney for the Eastern District of New York (Brooklyn). In her confirmation hearing to serve as US Attorney General under President Obama, Lynch confirmed that Sater did in fact work with the FBI “and other agencies”—presumably the CIA—in “providing information crucial to national security.” Where and how Sater gathered the information that he provided, whether or not it involved contacts with the Russian FSB (the successor to the KGB) and GRU, and whether those agencies themselves established a covert connection with Sater is something that both Mueller and the US intelligence community ought to be looking at today, of course.

Sater’s connection with Trump starts in the mid-2000s, when Sater joined a real estate firm called the Bayrock Group, which had been founded in 2001 by Tevfik Arif, a former Soviet official from Kazakhstan. Arif hired Sater in 2003, making him the firm’s chief operating officer. The firm later set up its headquarters on the 24th floor of Trump Tower on Fifth Avenue, just below Trump’s own suite of offices. (Sater’s first office suite, with his criminal enterprise called State Street Capital, had its offices in a Trump-owned building, 40 Wall Street, in the mid-1990s.)

Over the next several years Arif and Sater, via Bayrock, started or collaborated with Trump on a series of hotel and resort projects in Fort Lauderdale, Phoenix, and elsewhere. Their most important collaboration was the development in 2005 of the Trump SoHo project, which, according to the Times’s 2007 exposé of Sater, was a “sleek, 46-story glass tower condominium hotel [then] under construction on a newly fashionable section of Spring Street.” New York magazine adds that, oddly enough, the Trump SoHo tower “happened to be directly across the street from the storage facility that had been Sater’s previous undoing.”

When told by the Times about Sater’s criminal past, Alex Sapir, president of the Sapir Organization, which was involved in the SoHo project, said, “This is all news to me.” At the time, though, Trump didn’t separate himself from Sater, mingling with him at the SoHo opening, hanging out in Colorado while working on another project, and—according to Sater, at least—regularly interacting.

“How did I get to Donald?” Sater asked New York magazine, with typical braggadocio. “I walked in his door and told him, ‘I’m gonna be the biggest developer in New York, and you want to be my partner.’” After that, Sater said, he’d frequently pop into Trump’s own office to talk about this or that deal. “Donald wanted me to bring deals to him,” Sater told New York. “Because he saw how many I put on the table at Bayrock.”

Sater and Bayrock sought to extend the Trump brand to Ukraine, Poland, and elsewhere—including Moscow. Around 2005, Sater identified a location for a Trump Tower in the Russian capital, and he says that he personally escorted Donald Trump Jr. and Ivanka Trump around Moscow back then—an assertion that neither of the Trumps have denied. Last January The New York Times reported, “During a trip in 2006, Mr. Sater and two of Mr. Trump’s children, Donald Jr. and Ivanka, stayed at the historic Hotel National Moscow opposite the Kremlin, connecting with potential partners over the course of several days.”

After the financial crisis of 2008, Bayrock ran into difficulty, and Sater went out on his own. According to New York, following his separation from Bayrock he went to work for the Trump Organization, even carrying a business card listing his title as “Senior Advisor to Donald Trump.” Despite that, Trump denies ever employing Sater directly.

Sater’s links to Trump in recent years are obscure. According to recent reporting by the Times and the Post, however, as recently as 2015-16, Sater and Cohen, Trump’s lawyer and the executive vice president of the Trump Organization, were working together on a Trump Tower Moscow arrangement, though that too didn’t pan out.

But Sater and Cohen would cooperate on another venture. Following Trump’s election, the two men worked together to develop a curious peace plan for Ukraine. In it, Sater and Cohen worked with Andrii Artemenko, a Ukrainian opposition politician who himself had a questionable past, having spent time in prison in Ukraine for an embezzlement scheme, according to the New York Times story last February that first broke the news of his collaboration with Sater and Cohen (the charges against Artemenko were eventually dropped). According to the Times, Sater met Cohen and Artemenko at a New York hotel just two blocks from Cohen’s current residence in Trump Park Avenue. Cohen, who’s married to a Ukrainian woman, has business ties there himself, having once tried to get a Ukrainian ethanol business off the ground.

In 2014, a popular revolt toppled Ukraine’s pro-Russian president, Viktor Yanukovych, who was replaced by another oligarch, the pro-Western Petro Poroshenko. Paul Manafort, the GOP operative who would later sign on as Donald Trump’s campaign manager, was on Yanukovych’s payroll for years, and when Yanukovych fled Ukraine for Russia, Manafort contracted with opposition politicians in Kiev to help build an anti-Poroshenko bloc—and Artemenko joined in. (Manafort, of course, is under intense scrutiny in the Russiagate investigation from Mueller and two committees of Congress over his possible role as a go-between in collusion between Russia’s spy network and the Trump campaign. In July, Mueller ordered a pre-dawn raid at Manafort’s Virginia home seeking evidence in the case, amid speculation that Manafort might “flip” and turn against Trump.)

According to the Times, the Artemenko plan—delivered to Sater and Cohen, and then to Michael Flynn, the short-lived White House national security adviser who was forced to resign in February—involved using unflattering or compromising information (kompromat) to help oust Poroshenko and then winning the support of a new Ukrainian government for a 50- to 100-year lease of Crimea to Russia—which in 2014 occupied and annexed Crimea, which for many decades had been part of Ukraine. Because the vast majority of Ukrainian political forces would never agree to surrender their claim to Crimea, the plan was considered a hopeless nonstarter by most experts familiar with the Ukraine crisis. Yet the role of Sater and Cohen, both Trump associates, contributed to the growing belief in Washington that Trump, who has steadily refused to criticize Putin for his authoritarian excesses, extrajudicial killings, and suppression of free expression in Russia, has questionable ties to Russia.

The plan went nowhere, however. According to the Times, Sater gave Cohen the proposal in a sealed envelope, who reportedly said he left it in Flynn’s office. But in an interview with HuffPost, Cohen said he never delivered the envelope. But that doesn’t quite jibe with the Times’s original report, which noted that when Flynn resigned (because of his own still unexplained conversations with then-Russian Ambassador Sergei Kislyak during the transition), Cohen was still waiting for a response, “hoping a new national security adviser will take up their cause.” So far, as far as we know, current National Security Adviser H.R. McMaster hasn’t responded to the idea, which is probably long dead.

Even allowing for Sater’s long-established record as a liar and self-promoter, there’s plenty here for Mueller and other investigators to dig into. And Sater, too, seems to believe that something big is coming. In his interview with New York magazine, he hinted ominously about the near future. “In about the next 30 to 35 days,” he told reporter Rice, “I will be the most colorful character you have ever talked about. Unfortunately, I can’t talk about it now, before it happens. And believe me, it ain’t anything as small as whether or not they’re gonna call me to the Senate committee.”