John Donald MacIntyre Gass, MD was one of the most significant figures to emerge in ophthalmology in the last 100 years. There could be few ophthalmologists who cannot attribute part of their increase in understanding of retinal disease to the influence of Don Gass. His insights opened up opportunities for many new effective therapies. He has influenced ophthalmic thought worldwide, if not by his presence as a visitor, then through his scientific publications, his outstanding books and the international fellows he trained. Like many distinguished physicians, Don Gass's clinical acumen was well grounded in his understanding of ocular pathology. This experience was gained under the mentorship of Lorenz E Zimmerman, MD, who trained a number of distinguished ophthalmologists, who subsequently became professors. Professor Gass passed away on February 26, 2005 at the age of 76 years from pancreatic carcinoma. With the demise of Don Gass, the world of ophthalmology has lost an extraordinary physician of great talent, commonsense and humility. On the other hand it has gained a generation of young ophthalmologists inspired by his example.