Gregorio Allegri (1582 – 7 February 1652) was an Italian composer and priest of the Roman School of composers. He lived mainly in Rome, where he would later die. By far the most celebrated composition of Allegri is the Miserere mei, Deus, a setting of Vulgate Psalm 50. The Vatican, wanting to preserve its aura of mystery, forbade copies but in 1770, 14-year-old Mozart on a visit to Rome with his father, heard it but twice and transcribed it faithfully from memory, thus creating the first "bootleg" copy.

More information for this classical composer and his music can be found at Wikipedia... Gregorio Allegri