In 1981 he was elected vice president of the Bundestag ( 1979-1981 ) and then served as Governing Mayor ( Regierender Bürgermeister ) of West Berlin ( 1981-1984 ) .
He was elected vice president of the Bundestag 1979-1981 , but did not stand for re-election , because he became the Governing Mayor ( German : Regierender Bürgermeister ) of West Berlin ( 1981-1984 ) .