My question is really about possible antecedents to holocaust deniers rather than holocaust deniers themselves.
General Eisenhower is widely quoted quoted as saying, of his visit to the camp near Gotha:
"I made the visit deliberately, in order to be in [a] position to give first hand evidence of these things if ever, in the future, there develops a tendency to charge these allegations merely to propaganda".
That seems remarkably prescient and, to me at least, unlikely to have been sui generis or said without context.
Do we know what he had in mind when he said that?
Was it born out of his war time experience with propaganda or were there holocaust denier equivalents in his time? What were their issues?
What factors are likely have influenced his desire to be in a position to give first hand evidence (as distinct from the desire just to visit the camps, which is understandable from his position of leadership)?
During World War I, all sorts of propaganda was used by both sides to vilify the other. In one of the most notorious pieces of false propaganda, The Times, on April 17, 1917, published a piece which suggested that Germans were using Allied corpses to create lubricating oil and pigs food.
When such atrocities were proven false, it cast a pale over future stories. As such, when reports of atrocities began leaking from Nazi occupied Europe, they were often cast aside as similar to the anti-German propaganda of WWI.
Blurring the line further, some of the reports did include pieces of the previous atrocity reports. This only made the accurate reports all the more difficult to believe.
Hence, when the Western Allied troops liberated concentration camps, even those who had kept up with the atrocities might not have truly believed them until they saw them.