I think we can look to the PreSocratics and see the trend towards rationalization beginning there and more so that Aristotle perhaps embraced and ushered forward materialism. I would point most specifically to the PreSocratic philosopher Thales (the first philosopher in the Greek tradition)  who looked for an explanation to describe the cosmos beyond mythology. The trend towards rationalization, I believe, started before Socrates. We see philosophers like Heraclitus (to name one)  trying to describe the cosmos in terms of elements not mythological beings. 

To me it appeared Plato used myth as a epistemological tool to persuade the "hoi polli" into a particular way of thinking. We see this in the idea of the Noble Lie and the use of The Myth Of Metals in the Republic to this exact end. Granted Plato was a dualist but I am not sure he would have been a lover of mythology other than its usefulness in disseminating a particular kind of knowledge forward.