"The beginning and end of all music," per Max Reger (4)
I believe the answer is:
bach
(Other definitions for bach that I've seen before include "endearing Welsh appellation" , "German composer, who had twenty children, d.1750" , "Goldberg Variations composer, d. 1750" , "Name of composing family" , "J. S. -, Ger. composer" .)