Franz Xaver Sussmayr studied music in Salzburg under Michael Haydn, then moved to Vienna and became Mozart's student and close collaborator. When Mozart died in 1791 with the Requiem unfinished, Sussmayr completed it. Every performance of the Mozart Requiem heard today is partly his work.
The Story
Franz Xaver Sussmayr came from Upper Austria and studied composition in Salzburg under Michael Haydn, the younger brother of Joseph Haydn and a significant figure in Salzburg's musical life. That Salzburg formation gave him a grounding in the same tradition that shaped Mozart, and when Sussmayr arrived in Vienna he quickly entered Mozart's circle, studying with him and assisting on opera rehearsals.
He was present during Mozart's final illness in late 1791. When Mozart died on December 5, leaving the Requiem (K. 626) incomplete, Constanze faced a practical problem: the commission from Count Walsegg required a finished work, and she needed someone who knew Mozart's intentions and style. She turned to Sussmayr.
His completion added the second half of the Lacrimosa, then composed the Sanctus, Benedictus, and Agnus Dei largely from scratch, drawing on Mozart's sketches and their conversations. Musicologists have argued for two centuries about where Mozart ends and Sussmayr begins, and several alternative completions have been recorded. But Sussmayr's version is the one that became the standard, and it is what audiences hear in almost every concert performance. His own music has not survived the repertoire. That one act of completion is his entire legacy.
