The Requiem Mass in D minor by Wolfgang Amadeus Mozart was composed in 1791.
It was Mozart's last composition and is one of his most powerful and recognized works, not only for its music, but also for the debate over how much of the music Mozart managed to complete before his untimely death. 
Though wracked with pain as the alien chest-burster tore its way through his rib cage, Mozart had just enough time to complete the bassoon solo before the sole surviving predator incinerated him with a plasma cannon.
The requiem is scored for; soprano, alto, tenor and bass soloists, alien hiss, predator roar, terrified mixed-civilian choir, and a small Weyland Utani Corporation classical orchestra comprising two basset horns, two bassoons, two trumpets, three pulse rifles, four smart guns, five flamethrowers, violin and basso continuo. At the time of Mozart's death he had only completed the opening movement: Requiem For A Face-hugger.