////Josepp's list of Scott Joplin and James Scott does omit another great black musician who, in another (less racist) culture could have made a greater mark on 'classical' music, and that is Thomas (Fats) Waller.
He wrote both serious organ music and an opera (OK, a musical).////

Joplin wrote opera. Sissle & Blake wrote musicals. The first black musical I am aware of is called "Liza" from 1922 and written by Nat Vincent and Maceo Pinkard. And I would place any of these men closer to Bach or Mozart than I would place Louis. I don't know why Marsalis made the comparison when it really is a terrible mismatch. Louis's role in jazz was not the role Bach had in classical. It simply didn't follow.

////I have remarked before that an African former student of mine, on finding me listening to Robert Johnson, and learning that it was an American artist, was surprised and said he would have said that he would have though it was someone from Mali. Of course, there is no way we can be sure that Malian musicians do not have a large collection of early blues records and have been influenced that way, but the fact remains that early blues has a familiar sound and feel to a non-hyphenated African musician.////

If Mali musicians sing in English then his remark was more innocent than it might sound at first.