Fast Company:

Meet Bob Messerschmidt.

Apple quietly acquired Messerschmidt’s startup in 2010 (after Messerschmidt sent Steve Jobs an unsolicited email, but that’s another story). Afterwards, Messerschmidt was placed on the Apple Watch team, where he led a group charged with architecting new sensor technologies for the device. The heart rate sensors on the Apple Watch we know today are the creation of Messerschmidt and his team.

Fast Company has another in their very good series of interviews with key people at Apple.