A former British intelligence officer now working for a private security-and-investigations firm produced the dossier of unverified allegations about President-elect Donald Trump’s activities and connections in Russia, people familiar with the matter say.

Christopher Steele, a director of London-based Orbis Business Intelligence Ltd., prepared the dossier, the people said. The document alleges that the Kremlin colluded with Trump’s presidential campaign and claims that Russian officials have compromising evidence of Trump’s behavior that could be used to blackmail him. Trump has dismissed the contents of the dossier as false and Russia has denied the claims.