Guy Moumineux was born in Paris in 1927 to a French father and a mother from the province of Alsace, which had been conquered by Germany in 1871, returned to France after World War I, and changed hands between the two countries during and after World War II. He was only 13 years old when German forces conquered France, and among many other French citizens he was conscripted into forced labor on behalf of the German war effort. Still a teenager, to avoid the drudgery of labor and to pursue vaguely romantic dreams of military glory, he decided to join the German armed forces. In his own telling, he first tried to join the Luftwaffe (air force), but ended up in the service of the Wehrmacht, ultimately joining the Gross Deutschland division and seeing extensive action on the Eastern Front during Operation Barbarossa (See: Background). It was at this point that he adopted his mother’s maiden name, Sajer, in order to come across as more German to his fellow soldiers, who often made fun of him for his French accent.

After the war, Sajer worked as an illustrator for books and comics and later achieved a degree of fame with the publication of Le Soldat Oublié (The Forgotten Soldier) in 1965.