I don't know about the book, but in the movie "Bram Stoker's Dracula", they did give an origin story. I'll tell it as best to my recollection.
Dracula was once a crusader, one who was quite famous for his ability to kill the enemy. As a sort of revenge, the Turks (or muslims; I don't remember the specifics) sent a letter to his home declaring he had fallen in battle. He rode home as soon as he heard it, to try and arrive before it did, but alas, he was too late. His betrothed read the letter, believed it to be true, and took a dive off her balcony.
Dracula arrived just in time to hear the news and visit her body in a local church. Adding insult to injury, the priest informed him that, since she took her own life, she was now damned to hell, and would never reach heaven.
Dracula did not take this well.
Right there and then, he renounced God, then performed a ritual of some sort that desecrated the church, declaring that the blood of all mankind, or something to that effect, was his, then drank something a good deal like it. It was only afterwards that he realized he had gotten himself cursed by God and would know neither peace nor love for the rest of his life.
Not a very uplifting tale, is it?
As a side-note, Dracula and his kind were not killed by sunlight. The nosferatu simply were not at full power during the day, being creatures of night. As such, the Count can walk through a crowd in broad daylight without so much as a wince.
Makes me wonder if the vampires you see in the
Blade movies and "Buffy" are sort of a weaker breed, scorned by the Count and his kin due to some ancient offense their ancestors committed.

It would make things very interesting. I'm planning on using the idea someday, once I get that comic idea up and running...
I'm lost. I've gone to find myself. If I should return before I get back, please ask me to wait. Thanks.