Yahoo News provides some further information about the man behind the Trump-Russia dossier, reporting that he is a former MI-6 officer who:
had worked as a consultant for the FBI’s Eurasian organized crime section, helping to develop information about ties between suspected Russian gangsters and FIFA, said one of the sources, who is directly familiar with Steele’s work.
....U.S. officials said his allegations were not easily dismissed, in part because Steele was a known quantity who had produced reliable information about Russia in the past. "He’s a meticulous professional, and there are no questions about his integrity,” said one U.S. official... "The information he provided me [about Russia] was valuable and useful.”
And the BBC's Paul Wood claims that former MI-6 officer isn't the only source for these allegations anyway:
ICYMI: BBC correspondent says there's more than one source, more than one tape & more than one date of allegations in Trump intel dossier pic.twitter.com/NQmHeMHDM5— Alastair Reid (@ajreid) January 11, 2017
Most of the stuff in the dossier is nonetheless probably wrong. The question is, is any of it right?