Twentieth Century Undead

As far as I know, the American comic book authors made Dracula a vampire. Maybe I'm wrong. And the historical prototype of Dracula, Vlad the Impaler, didn't drink blood. He had a different pastime – impaling people. Mostly Turkish and other Muslim prisoners. And he got his nickname ("Dracula") because he was a member of the "Order of the Dragon" (the only Orthodox equivalent of Western European knightly orders) and constantly wore some kind of attribute of this order. But I don't understand why they later turned him into a vampire.