Who was employed as a court composer by the same noble family for nearly thirty years?

Joseph Haydn:

Explanation:

was an Austrian composer of the Classical period. He was instrumental in the development of chamber music such as the piano trio. His contributions to musical form have earned him the epithets "Father of the Symphony" and "Father of the String Quartet".

Haydn spent much of his career as a court musician for the wealthy Esterházy family at their remote estate. Until the later part of his life, this isolated him from other composers and trends in music so that he was, as he put it, "forced to become original". Yet his music circulated widely, and for much of his career he was the most celebrated composer in Europe.

He was a friend and mentor of Mozart, a tutor of Beethoven, and the older brother of composer Michael Haydn.

Joseph Haydn

Explanation:

During the nearly thirty years that Haydn worked at the Esterházy court, he produced a flood of compositions, and his musical style continued to develop.