This myth begins at the very creation of man and of Lilith (the first woman created for Adam).
So God created man and woman in his own image and blessed them. Many have made her a model for feminism, because when Adam would not relent in his domination of her, she grew so angry that she uttered the Holy name of God and vanished.
God then had to make Eve for Adam, making her of his rib bone, so that she would be attached to him and not leave as Lilith had done.
Here, Lilith went out to the Red Sea, where she made a bargain with the Angels and she was allowed to stay out on her own, as a witch, and MOTHER OF ALL DEMONS.
Cain was the first born son of Adam and Eve. He was banished, with a mark, from the land of his parents because he killed his brother Abel in a jealous rage. He was cursed by God and was forced to stalk the fringes of civilization, fearful of the sun and ravenous for blood, as he was refused by nature for fruits and vegetables.
According to vampire legend, Cain wandered until he found Lilith by the Red sea. She took him in and showed him the power of blood. (The Tree of life represented in blood, and thus why drinking blood / being a vampire is such a big deal in a religious context).
From Cain and Lilith came a host of demons and vampires in vague myths. Lilith taught Cain many things, including how to use his blood to evoke mystic powers and how to create others of his kind. At first Cain refused to beget, believing it was wrong to curse the world with others of his kind. But eventually he grew lonely and brought three others into the Vampiric fold. These three in turn begat 13 more.
Cain outraged by this behavior, forbade the creation of any more progeny. Gathering his children and grandchildren to him Cain built a great city – The first city in the world – where vampires and mortals coexisted in peace.
Finally the city was overthrown – some say a natural disaster was the cause; others that a spurned child’s vengeful sorcery precipitated the cataclysm. Cain vanished into the wastes, never to be heard from again.
Three vampires of the second generation likewise disappeared into the mists of legends, and the children and grandchildren became the true vampires.