I was gonna say

Chuck Berry

Buddy Holly!!!!!!!!!!!!!!!

It's like a tree, there'd be no Beatles without Chuck or Buddy...

First, apologies for lack of paragraph spacing, this website no longer seems to allow me to create paragraph spacing! Always used to! Now ...

As vocalists can be counted as musicians -

For me -

Number One - Louis Armstrong - superlative trumpet/ cornet playing aside, Louis effectively invented the American popular singer. Everyone from Bing Crosby to Billie Holiday admitted major influence from Pops. Before him, I believe there were no widely popular black male vocalists on record and the white males all sounded reedy with tons of vibrato and had no real influence in later times.

So, from Bing, we get Frank Sinatra, probably Billy Eckstine and all the other crooners of then and now.

Louis also sang and played on a ton of blues records in the '20 and '30s, alongside the likes of Bessie Smith, so he could also have a claim as the most influential male blues vocal stylist up until Muddy Waters.

So, from Muddy, to Big Boy Crudup to Elvis to most of white rock n' roll as we know it. Elvis also comes down the tree through Frank Sinatra too.

I've long thought Howlin' Wolf owes something to Louis vocally, as kind of Pop's little brother who got broken down and busted in the Delta and howled his pain away .

So, from Louis to Wolf to Captain Beefheart (lord help us all).

I'd be surprised if Louis wasn't some influence on jump blues singers like New Orleans born Roy Brown and Atlanta's own Billy Wright, both of whom were major influences on Little Richard. I can hear a little Louis in Richard's gravelly delivery at times.

So, from Louis to Little Richard via jump blues. Then the young James Brown was a pretty strong Little Richard impersonator in his early days, even to the point of stealing Richard's band for shows and IIRC at times billing himself as Little Richard!

Without Little Richard (and Chuck Berry and Elvis), arguably no Beatles, so no British Invasion, hard rock, prog rock (as I see the Beatles as the godfathers of prog conceptually at least) or metal.

One can also arguably jump from Louis to Jimmy Rodgers to Woody Guthrie to Bob Dylan to folk rock and the singer songwriters of the late '60s and '70s.

I appreciate the above does generalise at times but imo the broad strokes of a vocal family tree starting with Louis Armstrong and going in several branches down to the present day can be persuasively argued.

[Edited 6/6/13 9:55am]