Philippe Hurbain got his first Mindstorms kit in 2000, and soon his electronics background pushed him to build new and original sensors for the RCX. His web site shows how to build these sensors and includes a lot of technical information on the original Mindstorms kit. In 2006, he was selected as a beta tester for the new NXT that he received several months before the official release.
Michael Gasperi has been an expert in LEGO Mindstorms sensors since they were first introduced in 1998. His popular web site and contributing chapters to Extreme Mindstorms (Apress, 2000) have guided many people through the process of building their own extensions to the kit.