Mozart Never Finished His Famous Requiem
Mozart died before completing his legendary Requiem Mass. The work was secretly commissioned by a nobleman who intended to pass off the masterpiece as his own original composition.
Count Franz von Walsegg was known for paying composers to write music he would claim as his own. He commissioned Mozart to write this funeral mass for his late wife, hoping to fool his musical peers. Because Mozart died suddenly, his student had to step in to complete the score. It remains one of the most haunting and mysterious works in the history of classical music.
Source: Requiem (Mozart)