Wednesday’s revelations that Attorney General Jeff Sessions met twice with Russian Ambassador Sergey Kislyak last year, on top of the conversations with Kislyak that forced Trump’s national security adviser Michael Flynn to resign last month, have cast an increasingly bright spotlight on the once low-profile Russian diplomat.* While diplomatic colleagues like Foreign Minister Sergei Lavrov and the late U.N. Ambassador Vitaly Churkin seemed to relish international media attention, Kislyak kept his head down for much of his career. That being said, he’s been closely involved in U.S.-Russian relations for more than 35 years, including some of the most contentious and controversial moments of the post–Cold War era.

The Minneapolis Star Tribune once described Kislyak as “jowly, stout, white-haired, like a Russian government official out of central casting.” The Washington Post called him “a dour diplomat of the Soviet school who is known in Brussels as a relentlessly negative presence.” The Russian media, by contrast, has called him “a large and jovial career diplomat with an easy smile and a fluent command of English.”

According to his official bio, the 66-year-old Kislyak, with a background in engineering, joined the Soviet foreign ministry in 1977. In 1981, he was posted to the United States for the first time, initially at the mission to the United Nations, and then at the mission in Washington. There, he worked on arms control and nuclear issues with the United States during the closing years of the Cold War. In 1986, just after the meltdown at the Chernobyl reactor, he assured the New York Times that ”We have very stringent safety designs for reactors in our country.”

During the early 1990s, as the Soviet Union collapsed, Kislyak was in Moscow, steadily rising through the ranks of the foreign ministry in several positions related to scientific cooperation and arms control. From 1998 to 2003, he served as Russia’s representative to NATO in Brussels as well as ambassador to Belgium. It was an interesting time to hold that job. During his first year, Kislyak was recalled to Moscow by Boris Yeltsin’s government in protest of NATO’s airstrikes in Serbia during the Kosovo crisis, the most serious rupture in Russian-Western relations since the end of the Cold War. By the end of his tenure, despite ongoing Russian objections to NATO’s expansion into Central and Eastern Europe, there was a new spirit of optimism around NATO-Russian relations with the arrival of a young and energetic new president named Vladimir Putin. A NATO-Russia Council aimed at bridging differences and hosting joint military maneuvers was established in 2002. “The beginning of the process is rather encouraging,” Kislyak told the Washington Post that year.

From 2003 to 2008, he was back in Moscow as deputy minister of foreign affairs. During this time, Moscow was increasingly at odds with Washington. Kislyak was described by the Jerusalem Post in 2007 as “the point man inside the Russian Foreign Ministry on the Iranian nuclear issue,” and he often pushed back on the Bush administration’s attempts to get the United Nations Security Council to sanction Iran. Despite the tensions, Kislyak was unfailingly diplomatic. In a 2007 Independent article on whether U.S.-Russia relations had receded to Cold War levels, he was quoted as saying, “Russia and the United States have many issues that we either co-operate on, or that we need to review our positions on. We are expecting a serious discussion on serious problems, both from the perspective of our own security and of European security.”

Kislyak returned to Washington, this time as ambassador, in 2008 after his predecessor, Yuri Ushakov, was recalled to Moscow to serve as a foreign policy adviser to Putin. In a speech in Minneapolis in 2009, Kislyak praised the Obama administration’s desire to “hit the reset button” on U.S.-Russian relations, saying, “We like this terminology, borrowed from the computer world. But we still need to work on old bugs and viruses that are still there … Russian-American relations have never been easy.”

Kislyak was involved in the negotiations for a spy swap after a network of Russian sleeper agents was busted by the FBI in 2010. He also defended Russia’s controversial decision to ban adoptions by U.S. parents in 2012, seen by many as retaliation for sanctions placed on Russian officials after government critic Sergei Magnitsky died in Russian custody. In 2014, Kislyak criticized the Obama administration for what he called “the revival of the Cold War mentality” over talk of sanctions because of the situation in Ukraine.

A friendlier relationship was on the horizon in 2016, when Kislyak sat in the front row at an invitation-only foreign-policy address by Donald Trump at Washington’s Mayflower Hotel, during which the candidate called for better relations with Moscow. Trump “made some intriguing points, but we need to understand what is meant in the implementation,” Kislyak told Politico after the speech. Trump’s son-in-law Jared Kushner also met with Kislyak at Trump Tower during the transition.

Nothing in Kislyak’s biography jumps out as particularly suspicious or unusual for someone in his position, but it’s not unheard of for diplomats to have a side hustle in espionage. Could the quiet ambassador be involved in some clandestine activities? According to a CNN report on Thursday, Kislyak “is considered by US intelligence to be one of Russia’s top spies and spy-recruiters in Washington.” The Kremlin denied that he has intelligence links. But this isn’t the first time someone has suggested he might not be entirely on the up and up. In 2014, after an off-the-record lunch with Kislyak, Breitbart national security editor Sebastian Gorka mused suggestively about “what kind of person—working for what kind of agency—was assigned to represent the USSR at the United Nations in the 1980s as he was.” Gorka is now a high-level national security adviser to President Trump.

At this point, we don’t know if Kislyak is an intelligence agent. We also don’t know much about what the ambassador discussed with either Flynn or Sessions. All we know is that, in any Venn diagram of this increasingly multifaceted Trump-Russia story, Kislyak should be pretty close to the center.

*Correction, March 2, 2017: This article originally mischaracterized the contacts between Kislyak and Flynn. They were phone conversations, not meetings.