An explosive 35-page memo on Donald Trump’s relationship with Russia, which contains unverified allegations and which Trump called a "complete fabrication" Wednesday, was written by a former British intelligence officer working for Orbis Business Intelligence, Ltd., two people familiar with the matter told NBC News.

Separately, Rohit Kachroo, security editor for NBC News British partner ITV News, reported that the man's name is Christopher David Steele, a former officer with MI6 who was posted to Moscow in the 1990s. The memo was originally generated on behalf of Republican opponents of Trump's but was later shopped to the media by Democrats.

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Related: Trump Wasn't Told About Unverified Russia Dossier During Briefing, Official Says

Steele, now in his early 50s, was posted to Moscow and then to Paris. He set up Orbis in 2009. He and his business partner, former Foreign Office officer Christopher Parker-Burrows, established another company called Walsingham training in 2015.

Parker-Burrows spoke to ITV News outside his home in Winchester, England, but refused to comment regarding Steele and Orbis. One of Steele's neighbors told the Wall Street Journal that Steele would be away for a few days.

A two-page summary of the 35-page memo was included in supporting material prepared for the officials who briefed President-elect Trump on Friday about a U.S. intelligence report on Russia’s interference in the U.S. presidential elections, according to multiple officials. However, Trump was not orally briefed on the two-page "annex" outlining the allegations about him, according to a senior U.S. intelligence official with the knowledge of the preparation of the briefing. Trump said he learned the gist of the summary "outside that meeting."

The two-page summary about the unsubstantiated material was made available to the briefers to provide context for Trump should they want to draw a distinction for Trump between analyzed intelligence and unvetted "disinformation," according to the official. The briefers also had available to them unvetted "disinformation" about the Clinton Foundation, though that was not briefed to Trump either.

The existence of the two-page synopsis was first reported by CNN Tuesday afternoon. Their decision to report on the synopsis, as well as the publication of the complete 35-page memo by BuzzFeed, was harshly criticized by Trump. (BuzzFeed is partially funded by the parent company of NBC News.) "I think it was disgraceful, disgraceful that the intelligence agencies let any information that turned out to be so false and fake to get out," Trump said during his press conference in New York on Wednesday. "That’s something that Nazi Germany would have done and did do."

The memo, which suggested that Trump could be blackmailed by Russian intelligence, was circulated among Trump opponents over the summer and was eventually passed to the FBI. Republican Senator John McCain admitted Wednesday that he also passed the memorandum to the FBI.