I just looked through the historical sections of the relevant RFCs.
The hierarchical domain name syntax can be traced back at least as far
as a meeting on "Computer Mail" addressing held at the USC ISI in
Jan. 1982. RFC 805 is a report on the meeting, whose attendees
included numerous luminaries, including Jon Postel, who wrote RFC 805
itself, and Paul Mockapetris, the lead author of the final DNS RFCs.
It also contains assignments of further work for a lot of these folks;
Postel, for instance, is tasked with writing a report on what name
servers ought to do (and quite a few other reports as well).
This seems to be a fairly early working design document, as the
.com/.gov/.edu TLDs clearly had not yet emerged; the example is
phrased in terms of a .IN "Internet domain". However, the
hierarchical syntax is present, though it is not credited to any one
individual. So, the dot actually preceded dot com, and was cooked up
by one or more of the guys at the meeting (yes, to judge from the
names, they *were* all guys):
Duane A. Adams DARPA/IPTO Adams@ISI (202) 694-8096
Vint Cerf DARPA/IPTO Cerf@ISI (202) 694-3049
Harry Forsdick BBN Forsdick@BBN (617) 497-3638
Eric Schienbrood BBN shienbrood@bbn-unix (617) 497-3756
Bob Thomas BBN BThomas@BBND (617) 497-3483
Bob Fabry Berkeley Fabry@Berkeley (415) 642-2714
Bill Joy Berkeley unj@berkeley (415) 642-7780
Gene Ball CMU Ball@CMUA (412) 578-2569
Anil Agarwal COMSAT Agarwal@ISID (301) 863-6103
David L. Mills COMSAT Mills@ISID (202) 863-6092
Dave Crocker Univ. Del DCrocker@Udel (302) 738-8913
Ray McFarland DoD McFarland@ISIA (301) 796-6290
Dave Lebling MIT PDL@MIT-XX (617) 253-1440
Paul Mockapetris ISI Mockapetris@ISIF (213) 822-1511
Jon Postel ISI Postel@ISIF (213) 822-1511
Carl Sunshine ISI Sunshine@ISIF (213) 822-1511
Mark Crispin Stanford U. Admin.MRC@SCORE (415) 497-1407
Bob Braden UCL[A] braden@ISIA (uk) (01)387-7050
Steve Kille UCL UCL-Netwiz@ISIE (uk) (01)387-7050
Bill Tuck UCL UKSAT@ISIE (uk) (01)387-7050
Marv Solomon Univ. Wisc Solomon@UWisc
Ed Taft Xerox Parc Taft@Parc-Maxc (415) 494-4419
On the basis of the RFC itself, you can't really narrow credit down
farther than this, though of these individuals, Postel clearly had a
lot to do with actually making things happen.
Note that the then-current email addresses of these folks have '@'s,
but no '.'s. As another side note, the memo speaks uniformly in terms
of "computer mail"; the "email" contraction either hadn't been coined
yet, or wasn't considered suitable for formal usage.
rst