Christopher Steele, a British secret agent who spent his career in the shadows, has been thrust into the spotlight after an explosive dossier on Donald Trump was published Tuesday.

Christopher Steele, who wrote reports on compromising material Russian operatives allegedly had collected on U.S. President-elect Donald Trump, is a former officer in Britain's Secret Intelligence Service, according to people familiar with his career.

The purported Russian efforts were described in a newly released and uncorroborated dossier produced in August.