Ablamor of the Marsh
A knight who possessed a white hart which was killed by Gawain and Gaheris. In retaliation, Ablamor killed two of their greyhounds. Gawain challenged Ablamor to combat, Gawain was about to kill his opponent when his lady threw herself between them and Gawain killed her instead.
Horror-stricken by this Gawain could not continue, so Ablamor were spared.