One of Mozart's last works, this piece was written for the celebration of Holy Roman Emperor Leopold II of Bohemia's coronation, and the subject matter appropriately praises the titular emperor. Set in opera seria form (already considered old-fashioned by 1791), Mozart was in such haste to finish the work in time that he trusted the recitativo sections to his assistant Süssmayr, the man also later known for finishing his Requiem. However, its libretto updates, subtle orchestration, and virtuosic singing made this an extremely popular opera immediately following the composer's death.