Xotan, Duellist, Canadiest, et al: Dracula was, in fact, based on Vlad the Impaler, who was quite real, and who, like his Kuman ancestors, drank the blood of his dying enemies from a cup as a final act of vengeance. He did return after a long absence after being presumed (or hoped) dead; he had actually been imprisoned by the King of Hungary for (according to the Russian chronicles) threatening to impale him, and was released only after agreeing to marry the King's disagreeable (accounts vary) daughter or niece. It's possible that Stoker thought this Kuman blood-drinking custom, coupled with that business at the Scholomance, primed him to transition smoothly into his vampire half-life when his mortal life ended. But this was not the only source of Stoker's character.
Russian legend records another transformative character, a were-bird called Nightingale-Bandit.
When he whistled, it was with a nightingale's whistle
When he roared, it was with a wild beast's roar
The feather-grass lay down before him
The somber spruce trees bowed their gallant heads
The meadow flowers shed their azure petals
And all the worthy folk were pierced by Death
Nightingale-Bandit could transform into a bird, as Stoker's character could into a bat, and though the relationship of the three young women to the Count is never defined in the novel, two resemble him, and Nightingale-Bandit had three grown and very formidable daughters. Similarly, the Count was vulnerable to wounding by day, in his human form, and it was in such form that Ilya Muromets wounded, and ultimately killed, the Nightingale-Bandit.