Irving's first book was Apocalypse 1945: The Destruction Of Dresden. It was critically acclaimed all over the world. His next book, Hitler's War, got him in hot water for the simple fact that he didn't mention the Holocaust in it once and every publisher he went to told him they wouldn't print the book. This of course brought the ire of the jews on him and they have smeared his name, imprisoned him, and drug him through court multiple times to try and break him.
The man is on his deathbed now and I cannot stress enough how important of an author he is. We owe him a great deal for putting forth such wonderfully researched material.

He does believe that Jews were killed en masse in WW2 but he doesn't think Hitler even knew about it. He also dismisses the 6 million number and gas chambers outright.

If you have any interest in WW2 history you really should be checking out his books and listening to him speak (plenty of videos on youtube)