Most Influential American Musician of All Time?

Leonard Bernstein in classical music. He was a

Conductor
Composer
Musician
Teacher and a very public advocate of classical music written in America.

In jazz I'd have to agree with other's nomination of Johnson, Armstrong and Ellington for their roles in contributing so much.

But if I can only nominate one who's music is still popular and regularily played it would have to be Bernstein. I don't listen to the fathers of jazz very often anymore important as their contributions may have been.

Tvad, FWIW I think your definition of 'musician' might be a bit narrow, especially in view of how it's defined in my dictionary, i.e. a composer or performer of music and as an alternative a performer esp of instrumental music.

Re Robert Johnson's importance (to me) I'd never heard of him 'til you mentioned him. I though you were referring to a relatively obscure jazz personality from early 1900, James P Johnson who was an African American composer and piano player who developed the Stride style of jazz piano. He also composed hit tunes, waltzes, ballet, opera and symphonic music. He taught Fats Waller and influenced Gershwin, Count Basie, Duke Ellington, Art Tatum and Thelonious Monk, ad infinitum.

LMAO at my own ignorance and willingness to sign on just to be equitable. I'm not into Blue's. I went straight from hillbilly ('folk music' for the elitists and 'blue grass' for the generic non-hillbilly) to classical and jazz. Who is Robert Johnson? :-)