I've visited Sheldon Brown's website (I don't know if what he compiled can be called a website - website seems too small for what he made available to bicycle hounds) hundreds of times. It is such an incredible collection of bicycle history, references, information... I know that Sheldon's website is the go-to place for just about anything that I'm trying to find related to the bicycle. Bead seat diameters for any tire/wheel size, Bridgestone catalog scans, bottom bracket axle lengths for cranks from the '80s... It is all there.
I never met/spoke to/e-mailed Sheldon, but by virtue of the tone of his website, the things he's written, he's one of those folks you feel you do know. Sheldon Brown passed away yesterday. He will be missed, but remembered.