The who is obvious - Dan Brown. The what is more difficult because, firstly, he's deliberately vague and secondly he's changed his tune since so many people started protesting his so-called scholarship. Early on he was publicly saying things like all of the history was true, 99% of it was true and that it wouldn't have been any different if he'd written it as non-fiction, though, so to claim that Dan Brown wrote and marketed the book as pure fiction is unsustainable. He clearly meant to portray the basis for his novel as fact. There can be absolutely no doubt about it. Just as there can be absolutely no doubt about the fact that there's barely a single historical claim in the book that actually stands the light of scrutiny.
Having said that, as I stated from the beginning in this thread I couldn't care less how many ignoramuses believe the so-called 'history' in the Da Vinci Code. I do consider Dan Brown to be duplicitous and to have a personal agenda which is inimical to our faith, however, and the book and film undoubtedly served to promote a quite staggering number of heresies. That's all very well for those who make no claim to be Christian but for someone like Tom Hanks, claiming as he does to be Orthodox, to take part in it is beyond the pale. I reserve by far my striongest criticism for his hypocrisy and unfaithfulness and, as I have heard nothing to the contrary even from those who attend the same church, for his priest's lack of an adequate response to that promotion of heresy on his part.
James