The Hitler Diaries of Konrad Kujau
When German weekly Stern and British newspaper The Sunday Times ran excerpts from Adolph Hitler's supposed private journals in 1983, people quickly began to question their authenticity. British historian Hugh Trevor-Roper had read through the diaries before they were published, but a day later said he had "misunderstood the nature of their procurement." Soon after, the West German government performed chemical testing on the documents and declared them total fakes, presumably based on the book, "Hitler: Speeches and Proclamations — 1932-1945."
So who was behind the deception? A West German journalist who'd exposed the "diaries" pointed the finger at a Nazi memorabilia dealer named Konrad Kujau. The dealer was arrested and, in 1985, Kujau was found guilty of fraud and sentenced to four and a half years in prison, but released after just three years.