The fugue became a very popular form of music in the Baroque period. It was often played after a prelude. The most famous composer of fugues was Johann Sebastian Bach. He wrote two books, each with 24 Preludes and Fugues, called "The Well-Tempered Clavier" (in German: "Das Wohltemperierte Klavier"). Each book has a prelude and fugue in a different major and minor key. He also wrote many Preludes and Fugues for organ, sometimes writing a passacaglia, fantasia or toccata instead of the prelude, as in the case of the famous Toccata and Fugue in D minor. 