There are two harmonica playing bluesmen known as Sonny Boy Williamson. They are colloquially referred to as Sonny Boy Williamson I and Sonny Boy Williamson II respectively, but are of no relation.
The two are easy to distinguish. Williamson I played the harmonica acoustically and was essentially a pre-War artist. Williamson II was entirely an electrified harpist, in the style of Little Walter, reflecting the advent of the jukebox and electrified instruments following World War II.
(Compare the albums Sonny Boy Williamson I ~~ Sonny Boy Williamson II)