The original author of Dia was:

Alexander Larsson <alexl@redhat.com>

The current maintainers of Dia are:

Hans Breuer <hans@breuer.org>
Lars R. Clausen <lrclause@cs.uiuc.edu>

Other authors are:

Cyrille Chépélov <cyrille@chepelov.org>
James Henstridge <james@daa.com.au>
Jerome Abela <abela@solsoft.fr>
Emmanuel Briot <briot@volga.gnat.com>
Fredrik Hallenberg <hallon@debian.org>
Francis J. Lacoste <francis@contre.com>
Steffen Macke <sdteffen@web.de>
Jacek Pliszka <Jacek@Pliszka.fuw.edu.pl>
Henk Jan Priester <hj@justcroft.com>
Alejandro Aguilar Sierra <asierra@servidor.unam.mx>
Hubert Figuière <hfiguiere@teaser.fr>
Alexey Novodvorsky <aen@logic.ru>
Patric Sung <phsung@ualberta.ca>
Robert Young <robert@young.dsto.defence.gov.au>
田郷 明 (Akira TAGOH) <tagoh@redhat.com>
Richard Rowell <rwrowell@bellsouth.net>
Frank Gevaerts <frank.gevaerts@fks.be>
M. C. Nelson <mcn@kobayashimaru.org>
Matthieu Sozeau <mattam@netcourrier.com>
Xing Wang <quixon@gnuchina.org>
Andrew Ferrier <andrew@new-destiny.co.uk>
Angus Ainslie <angusa@deltatee.com>
Alan Horkan <horkana@tcd.ie>
Martin Hans <opfinder@gmx.net>
Vadim Berezniker <vadim@berezniker.com>
Krzysztof Foltman <kfoltman@onet.pl>
W. Borgert <debacle@debian.org>
Luc Pionchon <luc@handhelds.org>
Maurizio Tidei <tidei@compal.de>
Sampo Kellomaki <sampo@iki.fi>
Grégoire Dooms <dooms@info.ucl.ac.be>
Moritz Kirmse <momomaniac@gmail.com>
Robert Staudinger <robert.staudinger@gmail.com>

Dia is documented by:

Henry House <hajhouse@houseag.com>
Judith Samson <judith@samsonsource.com>
Kevin Breit <battery841@mypad.com>
Alan Horkan <horkana@tcd.ie>