Among the Germans, I really like Heinz Waaske and Hubert Nerwin. Both of them were deeply involved in camera design and often stepped in to improve existing products.

Waaske, who designed the Rollei 35 and later the Rolleimatic, later went on to work for Blaupunkt, while Nerwin eventually joined Graflex and was responsible for the Combat Graphic. Nerwin's other work included changes to the original Contax I and development of the Tenax II. Nerwin also worked for Kodak. You can read about Hubert Nerwin here.

And read about Heinz Waaske here.