Lonnie Donegan was definitely the man. He introduced me to Leadbelly via Rock Island Line, Bring a Little Water Sylvie, Midnight Special and other cracking songs, and also to Appalachian Old Time via Cumberland Gap, Don't You Rock Me Daddy-Oh, although I didn't know where they were from until a lot later, when I heard Uncle Dave Macon etc.
A lot of his songs that didn't get to be hits were also classics at the time eg In The Evenin' When The Sun Goes Down, Aint No More Cane On The Brazos. Unlike other people making money out of folk music at the time, he didn't water them down - he had the talent to do them pretty straight and get away with it.
cheers
Ray