Oswald Arnold Gottfried Spengler (* May 29th, 1880 in Blankenburg am Harz, Brunswick; † May 8th, 1936 in München) is the Author of the often discussed, albeit rarely read Der Untergang des Abendlandes (The Decline of the West).
He wrote his Ph.D. thesis about the topic Der metaphysische Grundgedanke der Heraklitischen Philosophie (The Fundamental Metaphysical Thought of the Heraclitean Philosophy).
He always sharply attacked the Weimar Republic, their incompetence and corruption, but also condemned the Antisemitism of the Nazis and declined cooperating with them. Since then, Nazi Germany officially ignored him. However, he always was an admirer of Mussolini, who returned the favor. He's often associated with the "Conservative Revolution".
Shortly before his death, he predicted in a letter to Hans Frank, that the German Reich wouldn't exist in ten years anymore.