I never met Sheldon Brown, but I learned a great deal from him.
Sheldon developed a website, SheldonBrown.com, that had an incredible amount of technical information about bicycles and cycling. If I Googled for some information about one of my bikes, I often ended up consulting his site.
Sheldon passed away on Sunday, February 3, 2008, reportedly of a massive heart attack. May he rest in peace. [ via spare cycles and BikeRadar.com ]