"Robert Johnson (from whom all true blues springs) " Trane Fan
Actually this is a popular misconception. Johnson had many earlier and contemporary musicians that influenced him. Son House, Charlie Patton, Willie Brown, Tommy Johnson, Scrapper Blackwell, Black Bottom McPhail, Floyd Jones and more were around at the birth of the delta blues. The earliest was probably Charlie Patton who started recording a few years prior to Robert Johnson. They all shared and stole songs from one another. Tommy Johnson originated the song that became "Crossroads" and Scrapper Blackwell wrote the "Kokomo Blues" that Robert Johnson made into "Sweet Home Chicago"
Robert Johnson was a genius, but he had company. Scrapper Blackwell outshines him on the guitar. Son House and Charlie Patton probably influenced the development of the delta blues more, largely due to being around longer.
I have the complete works of Robert Johnson on two CDs as well as CDs by Scrapper Blackwell, Tampa Red and Charlie Patton, and anthologies of other artists. One good one to check out is "The Roots of Robert Johnson".