45 years ago today, the Sony introduced the Walkman. Sony never pursued patent protection on the Walkman, believing it to be an innovation, not an invention. However, al little more than two years earlier, in March 1977 Andreas Pavel filed a patent application for his “Stereobelt” in Italy, followed by applications in Germany, United States, United Kingdom, and Japan.

Negotiations between Pavel and Sony began in 1980 and ended in 1986 with Sony agreed to pay Pavel limited royalties for the sales of certain Walkman models sold in Germany. The second round between Pavel and Sony began in 1990 in England and Wales, ending in 1993 with the court holding Pavel patent invalid for being “obvious and not significantly inventive,” leaving Pavel with a seven-figure attorney fee award to pay. On appeal Pavel tried to show non-obviousness through the commercial success of the Walkman, but the court rejected this, instead attributing the success to Walkman’s form factor, minimal operating power, and ability to reproduce high-quality sound at reasonable cost as key reasons for its appeal and popularity. The third and final round began in 2004, with Pavel threatening to file infringement proceedings in the remaining countries where he held patent, and Sony reportedly agreeing to a cash payment in the “low eight figures” and ongoing royalties of the sale of certain Walkman models.

Pavel told The New York times that he approached several electronics manufacturers but said he was met with rejection and ridicule. “They all said they didn’t think people would be so crazy as to run around with headphones, that this is just a gadget, a useless gadget of a crazy nut.” 45 years later, it’s hard to find someone running around without headphones. So it is with inventors — they see what the rest of us miss.