These are the players who won an individual Grand Prix without losing a match. The records listed are the records against humans, that is, byes are ignored. It is possible that there are other instances of this happening in 1997-1999. As always, what draws were IDs involved some amount of guesswork.

Jon Finkel and Gan Yan are the only people to win every round they were paired in a GP. Walker MacMurdo and Steve Locke are the only two to win a GP undefeated from zero byes.

name	record W-L-D-ID	event	format
Jon Finkel	13-0-0-0	GP Boston 1998	Tempest block
Jim Herold	11-0-1-1	GP Oslo 1999	ULG Limited
Masayuki Higashino	9-0-0-4	GP Hiroshima 2001	INV limited
Jose Barbero	10-0-1-2	GP Porto Allegre 2004	COK limited
Marcio Carvalho	13-0-1-1	GP Lisbon 2005	BOK limited
Kenji Tsumura	12-0-1-1	GP Kuala Lumpur 2006	DIS limited
Tomoharu Saito	11-0-1-2	GP Singapore 2009	extended
Gaudenis Vidugiris	12-0-1-2	GP Denver 2011	MBS limited
David Shiels	11-0-3-1	GP Dallas-Fort Worth 2011	MBS standard
Richard Parker	16-0-0-2	GP Lille 2012	DKA standard
Reid Duke	13-0-0-2	GP Nashville 2012	DKA limited
Alexandre Darras	12-0-1-2	GP Manchester 2012	DKA limited
Walker MacMurdo	12-0-3-1	GP Auckland 2012	RTR standard
Dan Lanthier	12-0-2-2	GP Vancouver 2015	modern
Scott Lipp	13-0-1-2	GP Sydney 2016	EMN limited
Brad Nelson	13-0-0-2	GP Omaha 2017	AKH standard
Thiago Saporito	13-0-1-1	GP Las Vegas 2017 (limited)	AKH limited
Steve Locke	16-0-0-2	GP Minneapolis 2017	HOU standard
Gan Yan	16-0-0-0	GP Seattle 2018 (standard)	RIX standard
Eli Kassis	12-0-1-2	GP Oakland 2019	modern
Allen Wu	13-0-0-2	GP Las Vegas 2019 (limited)	MH1 limited
Dylan Nollen	15-0-0-1	GP Portland 2019	ELD standard

In the era of one-day SCG Opens, I know of 88 players who won undefeated. This is also a common occurrence at one-day Regional Championships—that is, those events where the number of Swiss rounds is tied to attendance. There are only two other two-day events in the database with an undefeated champion:

name	record W-L-D-ID	event	format
Autumn Burchett	14-0-0-1	2017 GB National Championship	XLN draft / standard
Marshall Arthurs	16-0-0-2	SCG Louisville 2018	modern

Additionally, three teams have gone undefeated in team GPs. I believe this list is complete.

name	record W-L-D-ID	event	format
Scott Johns Gary Wise Mike Turian	10-0-2-1	PT New York 2000	PCY rochester
Darwin Kastle David Humpherys Rob Dougherty	8-0-2	GP Columbus 2001	APC limited
Greg Orange Adam Jansen Andrejs Prost	14-0-1-1	GP San Antonio 2017	unified modern