The Requiem in D Minor, K 626 by Wolfgang Amadeus Mozart was left incomplete at his death on December 5, 1791. Until the late 20th century the work was most often heard as it had been completed by Mozart’s student Franz Xaver Süssmayr. Later completions have since been offered, and the most favorably received among these is one by American musicologist Robert D. Levin.
According to a contract that Mozart signed and, the Requiem was commissioned by Franz, Graf (count) von Walsegg-Stuppach. The count, it seems, pretended to have some compositional ability and liked to pass off the work of others as his own. The new requiem, intended as a tribute to the count’s wife, was part of that game. Therefore, he insisted that Mozart was neither to make copies of the score nor to reveal his involvement in it and that the first performance was reserved for the man who commissioned the piece
Here is Claudio Abbado to perform my favorite section of this work for you: