Pianist/composer/musical director John Lewis, vibraphonist Milt Jackson, drummer Kenny Clarke (later replaced by Connie Kay), and bassist Percy Heath formed the Modern Jazz Quartet in the mid 1950s and were still together in the mid '90s (after a six-year break). The group's popular chamber-jazz sound was informed by Lewis's extensive studies in European compositional techniques. Jackson died in 1999, definitively closing the book on the long-lived, enormously influential quartet.