Stefan Kudelski didn't set out to make a sound recorder. He was interested in robotics, and in the 1950s, one of the ways to create robotic memory was to use magnetic tape. As a student, working with that tape, he built a machine that doubled as a recorder. Nobody was interested in the robotics aspect of the project, he said later: "But people were very excited about the recorder that I created. So, I became a manufacturer of recorders. That's how it started."
This first recorder, the Nagra, was, in Kudelski's words, "just a gadget." The second was "very serious equipment." But the third one, built in 1961, when Kudelski was 27, was "a good machine."
The Nagra III was the first sturdy, portable recorder which could produce sound as good as studio sound. Before Kudelski made it, the film industry had to cart its sound equipment around in a truck. The cinematographer Walter Lassally remembered, years later, the first time he saw a Nagra III:
"I remember the first time I encountered a Nagra really close-up was in Greece, on one of my Greek films called Maddalena. The sound-man appeared on this pier of this little island where we were shooting, on Antiparos, carrying a Nagra over his shoulder and a small folding-stool—and he sat down and said, 'I'm ready!' And I was absolutely amazed, because it was unheard of for the sound to be ready before me."
Not only could the sound be ready quickly, the person holding it could move with it. You could hold the Nagra III while you were running after a shot and still get good sound. It also allowed directors to easily sync sound with film, and New Wave directors would later credit it as a key tool that let them do their more spontaneous work. For about 30 years, up until the 1990s, the Nagra was used on almost every film that was made. "There was virtually no film…that did not use the Nagra," one sound engineer told The New York Times.
Here it is in action: