Wolfgang Amadeus Mozart
Wolfgang Amadeus Mozart (1756-1791) was an Austrian composer, widely considered to be a musical genius and one of the most popular and famous composers of all time.
Since Zappa only liked 20th century composers Mozart wasn't a huge influence on his work.
"In every era there are some composers who have hits, and some who don't. They are both working at the same time. One of them winds up on a candy that you get when you go on an airplane when you come to Austria. The other one: one paragraph on back of a book someplace." (Zappa in an interview for Austrian television, 1984)
Also mentioned in This Ain't CNN.