Concerning the effort to recover rabbinic biographies, Professor Judah Goldin writes:
… Such works are hardly biographies in the serious sense of the word, … for not only do the primary sources disappoint us deeply in the amount of reliable historical detail they provide, but even as regards the opinions and teachings of the Sages, one is left to guess what is early and what is late. In short, there is practically no way to get at development, surely and desperately necessary for the historian and biographer. These books therefore are filled with speculation, sometimes plausible, sometimes not. As reflections of the author's own imagination and interpretation, however, and as collections of data about the specific sage, they are informative exercises.
My research exhibits, alas, the deplorable qualities to which Goldin points. At the same time, I have continued to reflect on what we know about Rabban Yohanan ben Zakkai. Here are some of the results.