Gil Evans (13 May 1912 in Toronto, Canada â€“ 20 March 1988 in Cuernavaca, Mexico) was a jazz pianist, arranger, composer, and bandleader, active in the United States. He played a seminal role in the development of cool jazz, modal jazz, free jazz and jazz-rock, and collaborated extensively with Miles Davis.
Born Ian Ernest Gilmore Green, his name was changed early on to Evans, the name of his stepfather. His family moved to Stockton, California, where he spent most of his youth. After 1946, he lived and worked primarily in New York City, living for many years at Westbeth Artists Community. 
Between 1941 and 1948, he worked as an arranger for the Claude Thornhill Orchestra. Evans' modest basement apartment behind a New York City Chinese laundry soon became a meeting place for musicians looking to develop new musical styles outside of the dominant bebop style of the day. Those present included the leading bebop performer Charlie Parker himself. In 1948, Evans, with Miles Davis, Gerry Mulligan, and others, collaborated on a band book for a nonet. The group was booked for a week at the "Royal Roost" as an intermission group on the bill with the Count Basie Orchestra. Capitol Records recorded 12 numbers by the nonet at three sessions in 1949 and 1950. These recordings were reissued on a 1959 Miles Davis LP titled Birth of the Cool.