The Steele Dossier is a collection of reports compiled by former British intelligence officer Christopher Steele. It was commissioned by the opposition research firm Fusion GPS during the 2016 U.S. presidential election to investigate ties between Donald Trump and Russia. The dossier contains unverified allegations about Trump's connections to Russian officials and potential misconduct. The dossier gained significant attention after the election and was used in various investigations, including those led by the FBI and Robert Mueller. While some claims in the dossier have been substantiated, others remain unverified, leading to ongoing debates about its credibility and impact on U.S. politics.