Joss's Vampire Theroy
For the backround of the vampire Joss took many things from ancient mythologys and some from the latter fictional works about vampires such as Stokers's Dracular
in a way Vampires go back to the days when the earth was ruled by demons thousends of years before humans. the world was like hell! But Milloions of the demon races got traped in other worlds and gradually Humans came along and became the dominent spices on earth. In those days there was the "Pure Vampire" something which really did look like a demon, all green with spike sticking out of them ect.., and they could not speak english (obvoiusly as this was billions of years before the language was invented) When angel visited the Demon world of pyella he litrually turned into this demon when he Vamped, all of his human qualities left him and the demon inside of him took compleate controll. The Vampires we know of today aroses because the original vampire demon bit one of the early humans and infected there blood with his that human bit another and enother untill there was a whole race of vampires as we know them. Ever since the this happend there has been one female who has been the slayer. the primevil(first ever)slayer is seen in the season 4 final.
Although he took some things from moden fictional works like the stake through the hart and garlic and not entering unless invited one thing he did take from early mythology was that A vampire was really a demon in a dead humans body. this made them vunreble and not so all-powerfull as Dracula, they cannot fly and cannot turn into mist and most cant controll a person.
When the carecter of dracula was introduced in the season 5 first episode he still displayed all of the qualitys that he had in the clasic novel but this was exsplained as it not beging because he was a vampire but simply gipsy magic and hypotisem which is why he is the only one to have leart it.