Vampires I guess. The idea of vampires as 'blood sucking undead humanoid creatures' originate from the story of 'Count Dracula'. I need not tell you that Count Dracula was written by Abraham(or Bram) Stoker. It was inspired from the life of the Romanian emperor Vlad III or Vlad Dracul III. The story of the 'Blood Countess' or Bathory too left its influence in the Goth subculture. And then there was The Frankenstein Monster, Dr.Jekyll and Mr.Hyde etc. I feel the dark, outcast lifestyles of these mythical beings is the inspiration behind the formation of the Goth subculture. I think modern Goth culture has crossed its barriers as a subculture. It has defined itself as a sufficient cultural entity, able to exist by itself. In short Goth, I'd say, is a combination of love/romance, horror, denial, pain, outcast lifestyle and old Gothic architecture. Some medieval age influences are there too. Look at a grey oil painting from 15th or 16th century... you'll find some leads.
That is fascinating stuff and you've given me some good leads too. Even when I wrote the question and used the word "subculture" I knew it was an insufficient word but I wanted the reader to be able to identify who I was talking about. Cheers!