The Yag-Ath Vermellus is older than creation, born into icy realms of ancient horrors, and driven by only two things: rage and ravenous hunger. And every so often, chewing a hole through into other worlds. Extruding vicious little bits of themselves into our universe, seeking out hope and light. Falling to Earth, it came into contact with some cavemen and it made the first vampire.
Major Story Arcs
Crown of Worms
The piece that fell to Earth had formed into a key. The bearer of the key had the ability to open a door to another dimension where giant worms were trying to find a foothold, instilling its hunger in the vampires it had created.
The vampire Le Fanu was seen as the bearer of the key, giving her extra powers. Vampirella gained possession of it after she seemingly killed Le Fanu. Dracula, afraid of its power, wanted the key for himself, so it wouldn't be used again. Le Fanu had survived her fight against Vampirella and again sought possession of the key. But instead of taking it for himself, Dracula planted the key on Vampirella's forehead, making her Yag-Ath Vermellus' chosen queen.
Thanks to Dracula's interference, Vampirella was able to overcome the influence of Yag-Ath Vermellus and defeated it on its own plane of existence.