In my opinion, Ellington did not define jazz. They said that because he was considered by
academics to be a so-called "serious" musician.

I believe jazz was defined by Louis Armstrong, Charlie Parker and New Orleans traditional music and be-bop. Coltrane has to be in there somewhere. Miles, because he
"edited" the solo.

Bix defined his era.

There can never be a single person to define folk music because that would belie
what folk music is, a product of many people over time.