Short answers, pulled from the story.
Johann Sebastian Bach wrote the first book of The Well-Tempered Clavier in 1722 while serving as Kapellmeister at the court of Prince Leopold of Anhalt-Köthen. The autograph manuscript dates to that specific year and bears a title page stating it was composed for the profit and use of musical youth desirous of learning.
Scholars have long debated whether Bach intended equal temperament or some form of unequal well temperament for his keyboard works. Modern analysis suggests otherwise than the presumed equal temperament, with Johann Kirnberger describing a method where all major thirds were sharper than pure.
Each book contains twenty-four pairs of prelude and fugue arranged across all major and minor keys. The first pair is in C major followed by C minor then D major and so on up to B minor ensuring every key has been represented exactly once.
Printed copies of both books did not appear until 1801 fifty-one years after Bach's death. Three publishers released them almost simultaneously in Bonn Leipzig and Zurich while Haydn and Mozart studied the work closely during the maturing of the Classical style in the 1770s.
The first complete recording of The Well-Tempered Clavier was made on piano by Edwin Fischer between 1933 and 1936 for EMI. As of 2013 over one hundred fifty recordings had been documented with pianist Natalya Pasichnyk releasing Rethinking the Well-Tempered Clavier in 2024 which won the Golden Medal at the Global Music Awards.