Jean-François Bouchard offers us the exciting biography of a man without whom the twentieth century might have escaped its most cruel phase. It is indeed Sacht Hjalmar (1877-1970) who was the financial reference of the Nazi regime, party of which he was not a member. With a simple and effective literary device, the author gives each chapter two successive narrators: the banker himself, then economic historian. Reading is simple, lively, varied and there are stories of historical objectivity counterbalancing reflections of this "banker of the devil." The afterword of this book, centered on the European economy of 2015, will age much faster and much less well documented although this historical biography.