John Aaron Lewis ( May 3 , 1920 â `` March 29 , 2001 ) was an American jazz pianist and composer best known as the musical director of the Modern Jazz Quartet . John Aaron Lewis ( LaGrange , Illinois , May 3 , 1920 â `` New York City , March 29 , 2001 ) was an American jazz pianist and composer best known as the musical director of the Modern Jazz Quartet .