Johann Sebastian was made organist to the Duke of Saxe-Weimar. At the Duke’s court there was a chapel with an organ. Bach composed many of his great organ works at this time. He became very famous as an organist and was invited to play in other big churches and to give advice on organ building. He was extremely good at improvisation. On one occasion he was in Dresden at the same time as a French organist named Louis Marchant. There was going to be a competition between the two men to see who was better at improvisation. Bach was practicing the day before and Marchant heard him. He realized that Bach would win, so he left.