Downeast Bob, I think you are talking about Joel Walker Sweeney (Roscoe Sweeney was a character in the old Buzz Sawyer comic strip), "Break'em up Joe," who is credited for having added the 4th string to the banjo. The thumb string is still found on some African instruments.
I believe that the tenor banjo is a turn-of-the-20th century invention, although 4-string banjos and guitars were around before that.
The 5-string is so unique that it, not the tenor or plectrum, is considered the indigenous American folk instrument.