Passacaglia and Fugue in C minor (BWV 582) is an organ piece by Johann Sebastian Bach. Presumably composed early in Bach’s career, it is one of his most important and well-known works, and an important influence on 19th and 20th century passacaglias: Robert Schumann described the variations of the passacaglia as “intertwined so ingeniously that one can never cease to be amazed.”

https://en.wikipedia.org/wiki/Passacaglia_and_Fugue_in_C_minor,_BWV_582