Sheldon was a passionate cyclist, photographer, musician, family man, and countless other persons all in one; he was a particular champion of fixed-gear riding, and greatly responsible, in my opinion, for its resurgence after decades of being the province of messengers, winter-training racers, and old codgers pottering about on England's byways.
Sheldon also amassed possibly the greatest database of cycling technical and historical references on the Internet, housed in the warren of sites he maintained for himself and Harris Cyclery, and which included anecdotes, humor, rare photos, and more.
Furthermore, Sheldon was immeasurably generous with his time and knowledge, answering phone calls and emails from sometimes hundreds of cyclists per day, while still working full-time at the bike shop.
He and I met only by email a few times, but his humanity and kindness always shone through his words, even when his life must have been deeply discouraging.
He was knowledgeable, generous, straightforward, a real mensch. Cycling is far the better for his having been with us.