Elton Mayo
Mayo was neither an industrial psychologist nor a sociologist. See David Cullen's dissertation, A new way of statecraft: The career of Elton Mayo. Proquest Dissertations and Theses. Mayo earned a BA in philosophy and psychology at Adelaide (where the ICOH-WOPS conference will be held in September 2014). That was the highest degree he earned. If you want to learn how he got a position at HBS, read this terribly interesting dissertation.