Which composer wrote the Requiem in D minor, catalogued as K. 626?

Wolfgang Amadeus Mozart wrote the Requiem in D minor, catalogued as K. 626. Mozart began the commission in 1791, during the final year of his life, but he died before completing the score. His pupil Franz Xaver Süssmayr later finished the work, using Mozart’s sketches and instructions.

The Requiem was commissioned anonymously by Count Franz von Walsegg, who intended to present it as his own composition in memory of his wife. The mysterious messenger who approached Mozart helped create later legends about the work, although the historical circumstances are now better documented.

Mozart completed the opening movement, the Requiem aeternam, and left substantial material for other sections. Süssmayr supplied several passages and completed the orchestration and structure of the performance version most commonly heard today.

Because of this shared history, descriptions sometimes oversimplify the work by calling it entirely Mozart’s or entirely Süssmayr’s. The standard answer identifies Mozart as its composer, while acknowledging Süssmayr’s essential completion.