1. Pythagoras (c. 570 - c. 495 BC). The ancient greeks were very serious about their music. For instance, they developed an advanced musical notation, some manuscripts even exist today. Pythagoras discovered the connection between math and music, and (the far out) concept of the music of the spheres.
Atrium Musicae de Madrid - Musique De La Grece Antique
2. Pope Gregory I (c. 540 - 12 March 604). The gregorian chant guy.
Benedictine Monks of Santo Domingo de Silos - Chant - 1973
3. Johann Sebastian Bach (1685 - 1750). Pivotal figure in classical music. Explored music.
Wikipedia: "Scientist and author Lewis Thomas once suggested how the people of Earth should communicate with the universe: "I would vote for Bach, all of Bach, streamed out into space, over and over again. …