Most Influential American Musician of All Time?

I would name Duke Ellington, Sinatra, Miles Davis, Bill Evans and John Coltrane. For the more recent major influences in jazz, I would say Michael Brecker.

There are probably different ones for different genres.
Armstrong, Presley, Dylan all deserve the nominations. One not mentioned so far is Gershwin. A man who conquered Broadway, Hollywood, and the Concert Hall. Left us memorable music and was adept at what he did.

Woody Guthrie the song writer.

Armstrong, Chuck Berry, and Hank Williams

Scott Joplin (ragtime) by a mile. While he was recognized in his time as a great piano player, he obviously had a white colaborator who wrote the music. It was said "the negro mind is not capable of such ingenuity". What BS!