Short answers, pulled from the story.
The Well-Tempered Clavier is a collection of preludes and fugues for keyboard by Johann Sebastian Bach, spanning BWV 846-893. It consists of two books, each containing 24 prelude-and-fugue pairs covering all 24 major and minor keys. Bach completed the first book in 1722 and the second in 1742.
Bach intended some form of well temperament or circulating temperament, allowing all 24 keys to be played without retuning. Scholars debate the exact system; modern consensus favors an unequal well temperament rather than equal temperament, which only became the standard keyboard tuning after Bach's death.
The Well-Tempered Clavier was first published in 1801-51 years after Bach's death, by three publishers almost simultaneously in Bonn, Leipzig, and Zurich. Before that, both books circulated in manuscript copies.
Mozart transcribed several of Bach's fugues for string ensemble, including BWV 853, 871, 874, 876, 877, 878, 882, and 883, and composed his own Fantasy No. 1 with Fugue, K. 394, under its influence. Beethoven played through the entire Well-Tempered Clavier by the age of eleven and later arranged BWV 867 for string quintet.
Chopin began his 24 Preludes, Op. 28, in 1835 inspired by Bach's model. Dmitri Shostakovich wrote 24 Preludes and Fugues as a close reference to Bach's structure. Vsevolod Zaderatsky composed a full cycle of 24 preludes and fugues in 1940 in Gulag camp conditions, though the work was not premiered until 2014.
Edwin Fischer made the first complete recording on piano for EMI between 1933 and 1936. The second complete recording was made by Wanda Landowska on harpsichord for RCA Victor in 1949 (Book 1) and 1952 (Book 2). As of 2013, over 150 recordings of the collection had been documented.