Original: Carl Maria Friedrich Ernst von Weber ( 18 -- 19 November 17864 -- 5 June 1826 ) was a German composer , conductor , pianist , guitarist and critic , one of the first significant composers of the Romantic school .
Simplified: Meyerbeer was going to finish it , but in the end it was Gustav Mahler who finished it and conducted the first performance of the completed work in Leipzig in 1888 .