As mentioned before, John Polidori wrote 'The Vampyre' in 1819, which is often regarded as one of the first original vampire stories in a more modern literary sense.
Often, the main character in the first original vampire story is the vampire itself. It's the central figure that drives the horror and the plot. There might also be a victim or a potential victim who is trying to escape the vampire's clutches.
One of the earliest known vampire stories is from ancient Mesopotamia. The 'Ekimmu' were considered undead spirits that could be somewhat similar to early vampire concepts. They were malevolent spirits of the dead that could cause harm to the living.
Well, in the first original vampire story, a key element is the idea of the undead. Vampires were often depicted as corpses that came back to life to feed on the living, usually on blood. Another element was their aversion to sunlight, which was seen as a purifying force that could harm or even destroy them.
It's really hard to say who the most popular OC is as it can vary from reader to reader. Some might like the ones with unique powers like a vampire OC who can control the elements. Maybe it's the character who has a complex backstory that involves a love - hate relationship with one of the main Twilight characters.
Bram Stoker is the well - known author of 'Dracula', a very important early vampire novel. Stoker's research into different cultures and superstitions, along with his vivid imagination, led to the creation of the complex and terrifying Count Dracula, who has since become an archetype for vampires in modern media.