Terry M. Christensen Oregon State University John Archibald Wheeler (1911–2008) was among the giants of 20th-century physics. Even so, Wheeler’s many contributions to the corpus of physics are, in my view, overshadowed by his contributions to the community of physicists. Here it is useful to bear in mind that knowledge is cumulative in nature. Today’s breakthrough is tomorrow’s building block, upon which future discoveries will be predicated. A proficient mentor, by contrast, may well have a multiplicative influence on generations of physicists. Indeed, Harriet Zuckerman, a sociologist of science who has studied the “master-apprentice” relationship in Nobel Laureates, traces an intellectual lineage in chemistry that stretches from the Nobelist Hans Krebs (1900-1981) through four generations of Nobel Laureates and three generations of eminent chemists all the way back to Antoine-Laurent Lavoisier (1743–1794). The practice of mentoring scientific apprentices is not exclusive to laboratory-based sciences. But Nobel Laureates are rare, and not every scientist who has made an outstanding contribution to the corpus of knowledge has earned this distinctive honor. So how, in the absence of a Nobel Prize, does one gauge proficiency in mentoring? For that matter, how does one distinguish mentoring from other forms of pedagogy, and what is the difference, if any, between mentoring in a theoretical discipline as against mentoring in an experimental discipline? These questions provide the context of my examination of John Wheeler’s work as a mentor to theoretical physicists. Before these issues could be addressed however, it was necessary to develop a census of students whom John Wheeler advised at Princeton University. This database would have to include two distinct populations advised by Wheeler; students completing a dissertation and those students completing a Senior Thesis (a requirement for physics majors at Princeton). Although the Seeley G. Mudd Manuscript Library at Princeton maintains an online database that identifies the advisor(s) for most Senior Theses, there are no known records of advising assignments for dissertations in physics. Therefore, in order to identify Wheeler’s students in a comprehensive fashion, it was necessary to perform content analysis of the acknowledgements in the 555 Ph.D. dissertations and the 661 Senior Theses that were submitted during John Wheeler’s years on the Princeton faculty (1938-1976). The number of Senior Theses also includes those that were submitted during 1986 through 1994, after Wheeler had returned to Princeton as an emeritus.. I developed a similar database involving 339 Ph.D. dissertations and 122 Master’s theses for Wheeler’s years at the University of Texas at Austin (197–1986). (Although Princeton did offer a Master’s degree in physics during Wheeler’s era, there was no requirement for a thesis.) Additionally, many of Wheeler’s thoughts regarding interaction with advisees and colleagues are jotted throughout his research notebooks which, especially in his later years, also serve as diaries and scrapbooks. These are kept with the bulk of Wheeler’s papers at the American Philosophical Society. There is also a small but important collection of Wheeler papers at the Archive of American Mathematics, Center for American History at the University of Texas at Austin. The vast majority of my research to date however, has been conducted at the American Philosophical Society and Princeton. Later this year, I will be reviewing the papers of Karl Herzfeld, Wheeler’s own dissertation advisor at Johns Hopkins, and a number of oral history interviews in which John Wheeler is a subject or a participant. These items are held at the Center for the History of Physics, Niels Bohr Library and Archives, American Institute of Physics. This has been a fertile research topic. I have been able to identify the more than 112 students that Wheeler worked with on an individual basis, many of whom continued collaborative relationships with Wheeler as well with as other former Wheeler apprentices. I can show that John Wheeler supervised well more than three times the number of Ph.D. students that one would expect from a professor at a major research university. Perhaps the two most telling indications of John Wheeler’s commitment to mentoring are evidenced by the following: At Princeton, John Wheeler advised more than twice as many Senior Theses as any of his colleagues, and at Texas only three members of the physics faculty advised more Master’s theses than John Wheeler, even though he was 65 years old when he began teaching there and 75 when he retired. Rather than the raw numbers, however, in all likelihood, the most dependable evaluation of mentoring effectiveness is given by a long-term survey of the oeuvre of former students. There are two criteria to be evaluated: the total number of publications and citation data for those publications. These statistics are important because a high number of publications suggests that the former student was instilled with professional standards of work that placed a high value on productivity. Similarly, a mentor’s effectiveness at impressing an aesthetic sense of important problems that are ripe for solution is indicated when we find former students who produce papers that are cited frequently. Here I employ the criteria used by the SLAC-SPIRES literature database to evaluate the significance of papers in High-Energy Physics. By this measure, papers that are cited 500 times or more are classified as “renowned”, papers cited 250–499 times are “famous”, and those cited 100–249 times are “very well known”. Lesser papers are classified as “well-known” (50–99 citations) and “known” (10–49 citations). The data for Wheeler’s students are impressive. In general terms, a sizable percentage of John Wheeler’s students have published more than 100 papers. Moreover, I find that 11 of John Wheeler’s students have authored or co-authored renowned papers, 9 more have authored or co-authored “famous” papers, and another 9 have contributed “very well known” papers. In sum, well more than half of John Wheeler’s former apprentices have made ‘very well known’ contributions to the corpus of knowledge in physics. These insights raise more questions. What qualities, personal as well as professional, enabled John Wheeler to have this measure of success as a mentor? How do Wheeler’s students compare with those of other giants of the era (e.g., Hans Bethe or Robert Oppenheimer)? Certainly, given the impact that a skillful mentor may have on his former students’ careers, and by extension the course of the discipline, this line of research is both daunting and promising. Fortunately, having learned many lessons in research efficiency as a PACHS fellow, and more significantly, with the professional networking that my fellowship has facilitated, I am optimistic about facing this challenge.