Who employed Bach while he wrote the Brandenburg Concertos?

The correct choice, the Prince of Cöthen, was indeed the employer of Johann Sebastian Bach during the time he composed the Brandenburg Concertos. This period was significant in Bach's career, as he served as Kapellmeister (music director) at the court of Prince Leopold of Cöthen from 1717 to 1723. The environment in Cöthen was conducive to Bach's composition of instrumental music since the prince was a patron who appreciated and supported the arts, especially orchestral music.

During his time there, Bach created several significant works, including the Brandenburg Concertos, which were commissioned by the Margrave of Brandenburg but written while Bach was under the patronage of the Prince of Cöthen. The concertos exemplify his mastery of counterpoint, orchestration, and form, showcasing the rich musical environment that the prince fostered in his court.