Complex sentence: Siegfried Köhler (30 July 1923--12 September 2017) was a German conductor and composer of classical music, who worked as general music director of opera houses such as Hessisches Staatstheater Wiesbaden and the Royal Swedish Opera.
Split into simpler sentences: Siegfried Köhler (30 July 1923--12 September 2017) was a German conductor and composer of classical music. He worked as general music director of opera houses such as Hessisches Staatstheater Wiesbaden and the Royal Swedish Opera.