Sajer states that he was an inhabitant of Alsace drafted into the German Wehrmacht at age 16 and subsequently fought in the elite Großdeutschland Division during World War II. After the war he wrote about his wartime experience on the Eastern Front in The Forgotten Soldier.

The accuracy or authenticity of the book has been disputed by some historians, due to some incorrect cited details, while other details are simply impossible to verify due to a lack of surviving witnesses and documents.

The most frequently cited inaccuracy was Sajer's statement that, after being awarded the coveted Grossdeutschland division cuff title, he and his friend were ordered to sew it on their left sleeves (when it was actually sewn on the right), an obvious error that critic Edwin Kennedy called "unimaginable" for a former member of such an elite German unit. The author also discusses campaign locations in vague terms and never with specific dates, some which contradict historical fact: for example, Sajer's assertion that during the summer of 1942 he was briefly assigned to a Luftwaffe training unit in Chemnitz commanded by famed Stuka ace Hans-Ulrich Rudel, when, (by Rudel's own testimony) his training unit was actually in Graz, Austria during all of 1942. Likewise, the names of most of Sajer's companions and leaders don't appear on official rolls in the Bundesarchiv, nor are they known to the Grossdeutschland Veterans Association, whose leader, Helmuth Spaeter, was one of the first to question whether Sajer actually served in the Division as he claimed.

However, some authors and other Großdeutschland veterans have testified to the book's historical plausibility, even if they cannot speak to the specific events in the book. Lieutenant Hans Joachim Schafmeister-Berckholtz, who served in the Grossdeutschland during the same period as Sajer, confirmed in a letter that he had read the book and considered it an accurate overall account of the Division's battles in the East, while also noting that he remembered a Landser named Sajer in his Panzergrenadier company (5th co), the same company number Sajer mentioned being assigned to (though there was more than one "5th Company" in the Division). Sajer himself struck back against implications of fraud or fiction by claiming that The Forgotten Soldier was intended as a personal narrative, based on his best personal recollections of an intensely chaotic period in German military history, not an attempt at a serious historical study of World War II: "You ask me questions of chronology situations dates and unimportant details. Historians and archivists have harassed me for a long time with their rude questions. All of this is unimportant. Other authors and high-ranking officers could respond to your questions better than I. I never had the intention to write a historical reference book; rather I wrote about my innermost emotional experiences as they relate to the events that happened to me in the context of the Second World War."Nash, Douglas E. "The Forgotten Soldier: Unmasked." Army History. United States Army Center of Military History, Summer 1997.

Sajer further stressed the non-technical and anecdotal nature of his book in a 1997 letter to US Army historian Douglas Nash, stating "Apart from the emotions I brought out, I confess my numerous mistakes. That is why I would like that this book may not be used under [any] circumstances as a strategic or chronological reference." Nash, Douglas E. "The Forgotten Soldier: Unmasked." Army History. United States Army Center of Military History, Summer 1997. After reading Sajer's latest letter, one of his staunchest critics...Grossdeutschland Veteran's Association leader Helmuth Spaeter...recanted his original suspicions of Sajer, noting "I was deeply impressed by his statements in his letter... I have underestimated Herr Sajer and my respect for him has greatly increased. I am myself more of a writer who deals with facts and specifics...much less like one who writes in a literary way. For this reason, I was very skeptical towards the content of his book. I now have greater regard for Herr Sajer and I will read his book once again."Nash, Douglas E. "The Forgotten Soldier: Unmasked." Army History. United States Army Center of Military History, Summer 1997.

One of Mouminoux's comics is "Kursk Tourmente d'Acier", about the Battle of Kursk from the point-of-view of a German foot soldier.

Dutch film director Paul Verhoeven has discussed with Mouminoux the possibility of turning The Forgotten Soldier into a film. BrusselsBdTour