Here is more from the New York Times:
An analyst who was a key contributor to Democratic-funded opposition research into possible links between Donald J. Trump and Russia was arrested on Thursday and charged with lying to the F.B.I. about his sources.
The analyst, Igor Danchenko, was a primary researcher for claims that went into the so-called Steele dossier, a compendium of rumors and unproven assertions suggesting that Mr. Trump and his 2016 campaign were compromised by and conspiring with Russian intelligence officials to help him defeat Hillary Clinton.
In February, [special counsel John] Durham used a subpoena to obtain old personnel files and other documents related to Mr. Danchenko from the Brookings Institution, where Mr. Danchenko had worked from 2005 until 2010.
The inspector general report also said that a decade earlier, when Mr. Danchenko — who was born in Russia but lives in the United States — worked for the Brookings Institution, a prominent Washington think-tank, he had been the subject of a counterintelligence investigation into whether he was a Russian agent.
Here is a previous NYT piece about the Brookings subpoena, which notes that during his time at the think tank, Danchenko put forward analysis embarrassing to Russian President Vladimir Putin. More specifically, he had evidence that Mr. Putin plagiarized parts of his dissertation. Danchenko and Brookings colleague Cliff Gaddy revealed their findings at a 2006 Brookings event.
In 2009, Danchenko apparently made a comment to two Brookings colleagues that had sounded like a solicitation to pay for unauthorized disclosures of classified information, according to NYT.
Danchenko also worked closely with Brookings scholar Fiona Hill, who served in the Trump Administration as deputy assistant to the president and senior director for European and Russian affairs on the National Security Council (NSC).
Here is Danchenko page on the Brookings website. His LinkedIn page says he started off as a senior research assistant at the think tank and later became a senior research analyst.