Just as people are curious about their family lineage, academics are curious about their intellectual lineages. An intellectual lineage is more complex than a family lineage in some ways, because of course while we're restricted to two parents, we are often fortunate to have many excellent teachers who contribute to our intellectual development.
Nevertheless, the usual tradition is to trace intellectual influences back through Ph.D., since that's the highest degree, and usually the one that people spend the most time on, and the one that typically establishes the closest working relationship between student and mentor.
I knew my Ph.D. supervisor, Dorothy Paul, worked with Don Kennedy. Don Kennedy is a pretty well known figure in science, because he edits the journal Science. But I couldn't find out in my digging who Don Kennedy worked with. I decided to use a rather old fashioned technique to find out: I wrote a letter.
To my surprise, considering how hectic being Science editor must be, Don Kennedy wrote me back a short but very nice letter back very promptly. To my surprise, he worked with Don Griffin, whose work is famous in biology. He demonstrated how bats found their way in the dark: by echolocating. In animal behaviour, he was also a strong advocate for the field that became known as cognitive ethology.
I have yet to work out who Don Griffin did his doctoral work with. May take a while, but I'll keep it in mind.