Chuck Berry & Billy Haley.
Steelers is right, Haley came before Elvis.
Rock Around the Clock was a VERY popular as was the Rockin 'n' Rollin "Maybellene"
John Lennon said it best:
"If you tried to give rock and roll another name, you might call it 'Chuck Berry'."
Of course, there's Bill Haley (The Father of Rock 'n' Roll) & his Comets. "Crazy Man, Crazy" was the first Rock 'n' Roll song to hit American charts.
So, fairly it's between those two.