Johann Sebastian Bach was a German composer and musician of the Baroque period. He is known for instrumental compositions such as the Brandenburg Concertos and the Goldberg Variations, and for vocal music such as the St Matthew Passion and the Mass in B minor. Bach's music is revered for its intellectual depth, technical command, and artistic beauty. He was a master of counterpoint—the art of weaving together multiple independent melodic lines. During his lifetime, he was respected as a virtuoso organist but was not widely recognized as a great composer; it was only in the 19th century that his work was rediscovered and hailed as foundational to Western music. His 'Well-Tempered Clavier' is considered one of the most important works in the history of the piano (and its predecessors).