Arthur Loesch
In the 1980's, he was principally responsible for resurrecting the low-powered, single-ended triode (SET) amp and high-efficiency speaker from obscurity. When many designers were simply reworking classic circuits from the 1930's-50's, he was one of the few people to actually come up with an an original concept for phono reproduction using the WE417A (or Nuvistor) front end.
Art's still active, but is not as well known today as he was when Joe Roberts was publishing Sound Practices, where his designs were regularly discussed.