Was Dracula always in human-form?
The story is based on Vlad Dracul, who was a real person. He was a warlord who lived in Transylvania (which is now part of Rumania) in the Middle Ages. He used to torture his enemies by impaling them on stakes (hence his other name, Vlad the Impaler) and was said to drink their blood. Over the centuries the story was embroidered until it became the classic novel by Bram Stoker. In this novel Dracula is one of the undead. He drinks the blood of his victims who waste away until they too become like him. He is human most of the time but can shape-shift to avoid detection. Any unexplaind death or epidemic was said to be the work of vampires. This was in an age when people were much more superstitious than today and believed in things like devils, evil spirits and the like. When people die their bodies go cold and pale and you cannot draw blood, because the circulation has stopped. So the assumption was that they had the blood sucked out of them.