Nikolaus Harnoncourt
In 1971, Harnoncourt started to work with the conductor Gustav Leonhardt.  They recorded all of J.S. Bach's cantatas. This project took until 1990 to finish.  He also recorded Bach's St. Matthew Passion.  He performed with many other orchestras, including the Royal Concertgebouw Orchestra.  Often they were orchestras who used modern instruments, but he tried to make them play with an understanding of a historical style (bowing, phrasing etc).  Like other musicians working with historical instruments, he gradually realized that music from later periods such as the Classical music period and even the Romantic period used to sound different from what we usually hear today.  He recorded the symphonies and concertos of Beethoven.  He received many awards for these recordings.