During the 1950s, Miles Davis was known for developing which new style of jazz?

Miles Dewey Davis III (May 26, 1926 – September 28, 1991) was an American jazz trumpeter, bandleader, and composer. He is among the most influential and acclaimed figures in the history of jazz and 20th century music. Davis adopted a variety of musical directions in his five-decade career which kept him at the forefront of a number of major stylistic developments in jazz.

Born and raised in Illinois, Davis left his studies at The Juilliard School in New York City and made his professional debut as a member of saxophonist Charlie Parker's bebop quintet from 1944 to 1948. Shortly after, he recorded the Birth of the Cool sessions for Capitol Records, which were instrumental to the development of cool jazz.

Cool jazz is a style of modern jazz music that arose in the United States after World War II. It is characterized by relaxed tempos and lighter tone, in contrast to the fast and complex bebop style. Cool jazz often employs formal arrangements and incorporates elements of classical music. Broadly, the genre refers to a number of post-war jazz styles employing a more subdued approach than that found in other contemporaneous jazz idioms.