The Thomas Cantor is first and foremost a cantor and a cantor is responsible for everything that is connected to music in a church. Thomas Cantor is a cantor, if he or she is the responsible cantor in the St. Thomas Church. In Leipzig the Thomas Cantor is appointed by the City Council. In Leipzig he is the creative head of the Thomas Choir as well. Bach was not only responsible for the music in the St. Thomas Church and the five main churches in Leipzig, but for all churches in Leipzig too. Today Georg Christoph Biller is officially the "sixteenth Thomas Cantor after Johann Sebastian Bach". Johann Sebastian Bach was as a musician, as a composer and as the Thomas Cantor so considerable, that all following Thomas Cantors since Bach are "numbered serially" and this is related to Bach's time in Leipzig.
99 Music Calendars, Composers Calendars and Bach Calendars