Ferdinand “Jelly Roll” Morton (1885–1941), a New Orleans pianist, claimed credit for having invented jazz. And to some degree, it was fair of him to think so—after all, his recordings with the group the Red Hot Peppers (1926–30) are among the earliest examples of disciplined jazz ensemble work. But in truth, the evolution of jazz from ragtime and blues was something that many musicians, in several cities, took part in. Most regard Morton as one of the founders of jazz, the other founders include Bennie Moten (1894–1935), Eubie Blake (1883–1983), Duke Ellington (1899–1974), and Thomas “Fats” Waller (1904–1943).

Some would go back even farther to trace the roots of jazz: From 1899 to 1914 Scott Joplin (1868–1917) popularized ragtime, which was based on African folk music. Even astute music critics may not be able to draw a clear-cut distinction between ragtime and early jazz. Both musical forms rely on syncopation (the stressing of the weak beats), and either style can be applied to an existing melody and transform it. The definitions and boundaries of the two terms have always been subject to debate, which is further complicated by the fact that some musicians of the time considered ragtime to be more or less a synonym for early jazz.

But there are important, albeit not strict, differences between the two genres as well: Rags were composed and written down in the European style of notation, while early jazz was learned by ear (players would simply show one another how a song went by playing it); jazz encourages and expects improvisation, whereas ragtime, for the most part, did not; and the basic rhythms are also markedly different, with jazz having a swing or “hot” rhythm that ragtime does not.

Whatever its origins, jazz became part of the musical mainstream by the 1930s and influenced other musical genres as well—including classical. American composer George Gershwin (1898–1937) was both a songwriter and composer of rags as well as a composer of symphonic works. Many of his works, including Rhapsody in Blue (1924) and his piano preludes, contain ragtime and jazz elements.

Perhaps more than any other composer and musician, Miles Davis (1926–1991) expanded the genre: Through decades of prolific work, Davis constantly pushed the boundaries of what defines jazz and in so doing set standards for other musicians.