The earliest easily available jazz recordings are from the 1920's and early 1930's. Trumpet player and vocalist Louis Armstrong ("Pops", "Satchmo") was by far the most important figure of this period. He played with groups called the Hot Five and the Hot Seven; any recordings you can find of these groups are recommended. The style of these groups, and many others of the period, is often referred to as New Orleans jazz or Dixieland. It is characterized by collective improvisation, in which all performers simultaneously play improvised melodic lines within the harmonic structure of the tune. Louis, as a singer, is credited with the invention of scat, in which the vocalist makes up nonsense syllables to sing improvised lines. Other notable performers of New Orleans or Dixieland jazz include clarinetist Johnny Dodds, soprano saxophone player Sidney Bechet, trumpeter King Oliver, and trombonist Kid Ory.
Other styles popular during this period were various forms of piano jazz, including ragtime, Harlem stride, and boogie-woogie. These styles are actually quite distinct, but all three are characterized by rhythmic, percussive left hand lines and fast, full right hand lines. Scott Joplin and Jelly Roll Morton were early ragtime pioneers. Fats Waller, Willie "The Lion" Smith and James P. Johnson popularized the stride left hand pattern (bass note, chord, bass note, chord); Albert Ammons and Meade Lux Lewis developed this into the faster moving left hand patterns of boogie-woogie. Earl "Fatha" Hines was a pianist who was especially known for his right hand, in which he did not often play full chords or arpeggios, playing instead "horn-like" melodic lines. This has become commonplace since then. Art Tatum is considered by many to be the greatest jazz pianist ever; he was certainly one of the most technically gifted, and his harmonic insights paved the way for many who came after him. He is sometimes considered a precursor of bebop.