An arrangement of one of his works called for an "Air on the G String", and he made a  Notebook for Anna Magdalena.
This person composed a work for harpsichord that consisted of variations on an aria for Count   Kaiserling. An arrangement of one of his works called for an "Air on the G String", and he made a  Notebook for Anna Magdalena. This man composed a work based on a theme provided to him by   Frederick the Great in the Musical Offering. This person also composed a work which included 24  preludes and fugues, one for each key, and he composed six concertos for the Margrave Christian  Ludwig. Name this Baroque composer of The Well-Tempered Clavier  and the Brandenburg Concertos.
This person composed a work for harpsichord that consisted of variations on an aria for Count   Kaiserling.
Johann Sebastian Bach [prompt on partial answer]