Harry Cox I think. While we're on this subject, I'm not impressed with some of the explanations of the song. James Reeves has the most unconvincing. Foggy Dew = Virginity (Whaaat?) This seems to have stuck though.
As far as I can gather the Foggy Dew is a corruption of The Bug-a-Boo i.e. The Bogey Man, or Boggart.
The original story is of two young wags, one of whom dressed up as a ghost, and terrified the young girl into the bed of the other one. This explains why she was so terrified in the middle of the night. Good plan if you're a young and stupid bloke. Never worked for me though! (Bugger!)