Russian intelligence knew exactly who Christopher Steele was in the early 1990s.

That was years before Steele's public outing as an MI6 agent in 1999 and decades before the British ex-spy compiled his salacious and unverified dossier on then-candidate Donald Trump using Russian sources.

The details about Steele’s career were outlined by Fusion GPS co-founders Glenn Simpson and Peter Fritsch in their new book, Crime in Progress: Inside the Steele Dossier and the Fusion GPS Investigation of Donald Trump.

Steele moved to Moscow with his wife, Laura, in 1990, and Russian intelligence tracked him closely while he worked under a diplomatic cover at the British Embassy.

“That cover wasn’t too deep: Steele would laugh when recalling the dopey mind games the KGB would play to remind him that he and Laura were under constant surveillance, once stealing her favorite dress shoes before a diplomatic dinner,” Simpson and Fritsch wrote.

Steele said the fall of the Soviet Union brought only brief respite, since he was under surveillance again within days.

“The intrusive tails and petty harassment were indistinguishable from Soviet practices,” the Fusion GPS founders wrote.

Steele returned to England in 1993 and moved to France in 1998. Steele’s chances of returning to Russia ended the next year.

“In 1999, a disgruntled former MI6 colleague posted on the Internet a list of 116 suspected MI6 agents,” Simpson and Fritsch said. “Most of the names were indeed spies operating under ‘light cover’ in British embassies overseas, as Steele had in Moscow in the early nineties.”

Steele then headed MI6’s Russia desk for years, leaving the spy agency in 2009 and founding Orbis Business Intelligence with Christopher Burrows, a fellow former British spy also outed the decade prior.

“Steele’s official government biography described him as a Foreign Office diplomat,” the Fusion GPS founders wrote. “But it was well known (at least in investigative circles) that his real employer was the United Kingdom’s Secret Intelligence Service.”

Simpson and Fritsch's Fusion GPS, working on behalf of Hillary Clinton's presidential campaign, hired Steele to investigate Trump's links to Russia.

Fiona Hill, formerly Trump’s top Russia adviser on the National Security Council, testified Steele’s dossier “very likely” contained Russian disinformation .