The Well-Tempered Clavier Book I: Prelude and Fugue in C minor, BWV. 847 by Johann Sebastian Bach
Bach wrote two books of preludes and fugues, each containing a prelude and fugue in all 24 keys. The first book was likely completed in 1722, and the second book completed in approximately 1742. The purpose of this collection was, according to Bach, “for profit and use of musical youth desirous of learning, and especially for the pastime of those already skilled in this study”.