Complex sentence: Until 1985 the singspiel was stage-managed by Olf Fischer, then, until 1988, by the leading BR entertainment head Helmut Kirchhammer, who also guided the team of authors.
Split into simpler sentences: Until 1985 the singspiel was stage-managed by Olf Fischer. Then, until 1988 it was the leading BR entertainment head Helmut Kirchhammer, who also guided the team of authors.