Johann Sebastian Bach (German: [ˈjoːhan zeˈbasti̯an baχ]) (31 March [O.S. 21 March] 1685 – 28 July 1750) was a German composer and musician of the late Baroque period. He is known for his prolific output across a variety of instruments and forms, including the orchestral Brandenburg Concertos; solo instrumental works such as the cello suites and sonatas and partitas for solo violin; keyboard works such as the Goldberg Variations and The Well-Tempered Clavier; organ works such as the Schübler Chorales and the Toccata and Fugue in D minor; and choral works such as the St Matthew Passion and the Mass in B minor. Since the 19th-century Bach Revival, he has been widely regarded as one of the greatest composers in the history of Western music.

The Bach family had already produced several composers when Johann Sebastian was born as the last child of a city musician, Johann Ambrosius, in Eisenach. After being orphaned at age 10, he lived for five years with his eldest brother, Johann Christoph, then continued his musical education in Lüneburg. In 1703 he returned to Thuringia, working as a musician for Protestant churches in Arnstadt and Mühlhausen, and for longer periods at courts in Weimar, where he expanded his organ repertory, and Köthen, where he was mostly engaged with chamber music. In 1723 he was hired as Thomaskantor (cantor at St Thomas's) in Leipzig. There he composed music for the principal Lutheran churches of the city and its university's student ensemble, Collegium Musicum. In 1726 he began publishing his organ and other keyboard music. In Leipzig, as had happened during some of his earlier positions, he had difficult relations with his employer.