Hilary Stone is one of those semi-legends in the hobby. He's been a collector/dealer for years, nay, make that centuries; has a knack of coming up with incredibly rare and offbeat equipment, and is a font of knowledge par excellence. Rumor has it that he knows lots of stuff that Sheldon Brown has never heard of

.
He's both a collector and a dealer. His prices are usually quite reasonable and he seems happy to go with the flow of the market, rather than attempting to pump up new and unreasonably higher prices. Above all, he seems to have that knack of coming up with the kind of stuff that I'd love to own, but don't have the slightest clue (nor the patience to find the sources) on how to find.
All in all, a good guy. Spent a year on CR, and never heard a nasty comment about him. That, in itself, is pretty incredible.