Simplify the following text for a Grade 8 native English-speaking person.
Original: The Requiem Mass in D minor K626 is a famous piece of music by Wolfgang Amadeus Mozart which he composed in 1791 .
Simplified: The Requiem Mass in D minor ( K. 626 ) by Wolfgang Amadeus Mozart was composed in Vienna in 1791 and left unfinished at the composer 's death .