Aleck "Rice" Miller used the name 'Sonny Boy Williamson' at the behest of King Biscuit Flour for whom he did a regular radio show. He could not legally record under that name until after the murder in 1948 of John Lee Curtis "Sonny Boy" Williamson the original artist using that name.
Which Sonny Boy is this? From the voice, I originallyt assumed it must have been Sonny Boy 1, but then there is the audience applause to suggest that this must be Sonny Boy 2, since the original surely never got recorded in concert? Anyway. excellent harp work, which suggests that it probably is Sonny Boy 2, since they both can't have been that good.