Task: Question Answering
Input (English): Passage: As far as we know, the earliest cantatas of Johann Sebastian Bach were performed in Mühlhausen from 1706 to 1708. He was employed as an organist there, but he occasionally composed cantatas, mostly for special occasions. The cantatas were based mainly on biblical texts and hymns, such as Aus der Tiefen rufe ich, Herr, zu dir, BWV 131 (a psalm setting), and the Easter chorale cantata Christ lag in Todes Banden, BWV 4.
Bach was next appointed organist and chamber musician in Weimar on 25 June 1708 at the court of the co-reigning dukes in Saxe-Weimar, Wilhelm Ernst and his nephew Ernst August. He initially concentrated on the organ, composing major works for the instrument, including the Orgelbüchlein, the Toccata and Fugue in D minor, BWV 565, and the Prelude and Fugue in E major, BWV 566. He was promoted to Konzertmeister on 2 March 1714, an honour that entailed performing a church cantata monthly in the Schlosskirche. The first cantatas he composed in the new position were Himmelskönig, sei willkommen, BWV 182, for Palm Sunday, Weinen, Klagen, Sorgen, Zagen, BWV 12 for Jubilate Sunday, and Erschallet, ihr Lieder, BWV 172, for Pentecost. Mostly inspired by texts by the court poet, Salomo Franck, they contain recitatives and arias. When Johann Samuel Drese, the Kapellmeister (director of music), died in 1716, Bach hoped in vain to become his successor. Bach looked for a better position and found it as Kapellmeister at the court of Leopold, Prince of Anhalt-Köthen. However, the duke in Weimar did not dismiss him and arrested him for disobedience. He was released on 2 December 1717.In Köthen, Bach found an employer who was an enthusiastic musician himself. The court was Calvinist, therefore Bach's work from this period was mostly secular, including the orchestral suites, the cello suites, the sonatas and partitas for solo violin, and the Brandenburg Concertos. He composed secular cantatas for the court for occasions such as New Year's Day and the prince's birthday, including Die Zeit, die Tag und Jahre macht, BWV 134a. He later parodied some of them as church cantatas without major changes, for example Ein Herz, das seinen Jesum lebend weiß, BWV 134. 
Question: What position was held by the man that Bach served as Kappelmeister for?
Output (English): Prince of Anhalt-Köthen.