Miles Davis is arguably the most influencial Jazz musician of the 20th century. After playing with the beboppers including as a sideman with Charlie Parker he was at the forefront of Cool Jazz, Hardbop, modal jazz, and Jazz/rock/fusion. He lead several of the most influencial jazz bands ever. He helped to define the careers of several musicians who are now legends themselves. I can't think of any other musician that has been as important to so many different subsets of jazz and for such a long time. I know not everyone likes Miles but he is not just one thing.