Mel Wacks writes:

In 1985 Bowers & Merena published a limited-edition (500 copies) book entitled Abe Kosoff: Dean of Numismatics, in conjunction with its auction of Kosoff's estate. (A review and discussion of the book was posted on the PCGS coin forum a few years ago).

In the book's front matter, author Q. David Bowers noted the following:

In 2005 I began using the sobriquet "Dean of American Numismatics" when referring to QDB himself. (Incidentally, I feel the term is well justified, in the sense that Dave has significant authority over the subject matter of numismatics. Not sole authority, of course; and not the longest active experience as a professional numismatist [Harvey Stack was working full-time for the family firm in 1947]; but certainly he's a significant force in the numismatic world.)

As for the terminology itself, there can be deans of people (e.g., of men, of women, of freshmen, of architects, or even of numismatists, I suppose), deans of campuses, deans of schools or programs, and deans of subject matters. Probably other kinds of deans, as well. Dean Martin comes to mind. A "Dean of American Numismatics" might be akin to a "Dean of Engineering" --- just with more Buffalo nickels lying around his office.

To read the PCGS coin forum post, see:Abe Kosoff: Dean of Numismatics--A book review and commentary(forums.collectors.com/messageview.cfm?catid=26&threadid=558941)