Meet Sergey Kislyak, the Russian ambassador everyone says they haven't met

Russian Ambassador Sergey I. Kislyak is back in the limelight, bringing a second Trump official into a delicate situation.

Trumpworld: First there was retired Gen. Michael Flynn, who lied about his phone conversations with Kislyak, and ultimately resigned from his position as National Security Advisor. Second was Attorney General Jeff Sessions, who claimed he hadn't met with any Russians, then admitted he'd twice met with Kislyak. He's also met with Jared Kushner, in addition to two other Trump campaign members.

Democrats: Sen. Claire McCaskill falsely tweeted Thursday that she had never met with him, and Politico reported on Friday that Kislyak met with Nancy Pelosi, who earlier claimed they hadn't.

So who is this man who has gotten so many U.S. officials in trouble?

• He's been accused of being a Russian spy by some in the U.S. intelligence community, but there has never been any proof, per CNN.
• He is carefully watched by the U.S. intelligence community, according to Russian officials who talked to NYT.
• Before Putin came to power, Kislyak often hosted parties at the Russian embassy's estate in Maryland, which Obama shut down as part of the sanctions against Russia late last year.
• 35 of Kislyak's team members were sent back to Russia in December when Obama imposed sanctions.
• Kislyak is a physicist, which helped him with arms-control negotiations.
• He was an ambassador to Belgium and worked for the UN.

• Until now, he hasn't been viewed as a high-profile ambassador.
• He has told his associates that he'll probably leave the U.S. soon and is shocked by how many people avoid communicating with him now, according to NYT.

When asked about his interactions with American officials during a speech at Stanford in November, Kislyak said:

"It is normal diplomatic work that we have been doing: It is our job to understand, to know people, both on the side of the Republicans and Democrats. I personally have been working in the United States for so long that I know almost everybody."

Why it matters: Kislyak was doing his job. Ambassadors meet with politicians. The problem is that Flynn, Sessions, Kushner, McCaskill and Pelosi felt the need to hide their communications with him.