Walter Friedrich Otto (1874–1958) was one of the most outstanding representatives of German twentieth-century Altertumswissenschaft. Moreover, he played a prominent part in entire German culture of the period as an impressive humanist deeply convinced about the significance of Greek culture for modern European culture as a whole and, in particular, for German humanism. His theoretical interests in religious beliefs were enrooted in the philosophy of Friedrich Nietzsche and close to Martin Heidegger. Otto embarked upon his scientific path by pursuing Latin studies and linguistics; previously, he studied Roman and, subsequently, Greek religions, perceiving the latter as a supreme achievement of religious thought, and claiming that the foundation of Greek polytheism was a religious attitude toward Being (das Sein), which he contrasted with Christianity. In doing so he considered himself to be a polytheist and a pantheist, in the manner of Goethe. German experts on classical culture for long treated Otto’s interpretations sceptically or outright grudgingly, and Martin Nilsson, regarded as a great authority, harshly assessed his Dionysus (first edition: 1933), today recognised as a classic. In contrast to Nilsson, Otto’s interpretation of Greek religion emphasised intense and authentic religious experience, which became the substance of the “vision” (das Schauen) of the believer. Cooperation with the acclaimed ERANOS group produced Otto’s brilliant study: Der Sinn der eleusinischen Mysterien (its English translation: The Meaning of Eleusinian Mysteries, was published in 1955), to this day extremely important for all dealing with this range of problems owing to the fact that it drew attention to the significance of religious experience in rites celebrated in the Eleusian telesterion. Today, Walter F. Otto is acknowledged as one of the “great four” of twentieth-century classical scholars dealing with Greek religion, on par with Károly Kerény, Jean-Pierre Vernant, and Walter Burkert. Familiarity with his conceptions, entire oeuvre, and specially, apart from Dionysus, his book: Die Götter Griechenlands, is absolutely indispensable for those wishing to earnestly study the religion of the ancient Greeks.