Here’s his wikipedia page

NY Times obituary if you want an idea of how the West portrayed him

Another wiki page about Cambodian genocide denial including this banger:

On June 6, 1977, Noam Chomsky and Edward S. Herman published an article in The Nation which contrasted the views expressed in books by Barron and Paul, Ponchaud, and Porter and Hildebrand, and in articles and accounts by Butterfield, Bragg, Kahin, Cazaux, Shanberg, Tolgraven and others. Their conclusion was: “We do not pretend to know where the truth lies amidst these sharply conflicting assessments; rather, we again want to emphasize some crucial points. What filters through to the American public is a seriously distorted version of the evidence available, emphasizing alleged Khmer Rouge atrocities and downplaying or ignoring the crucial U.S. role, direct and indirect, in the torment that Cambodia has suffered.”