Two legends that I have heard of are:
Adam's first wife, Lilith, was expelled from Eden for refusing to "submit" to her husband. She wandered out into the wastelands and mated with fallen angels or supernatural beings of some sort, and her offspring became all of the demons and vampires.
The second one is that Judas was the first vampire, cursed to never die or see the light of day until the Second Coming. His tie in with the Crucifixion explains why the cross and other holy relics can repel and even kill his descendants. The wooden stake was originally a branch from the tree from which he hanged himself, but has become simply any type of wood.
On a somewhat similar note, Dracula was never bitten by another vampire, but was, instead, transformed by making a pact with Lucifer, basically becoming his son, and the satanic equivalent to Christ.