Originally, Vampirella believed that she came from the planet Drakulon, an idylic world where blood ran like water. Paradise was lost however when it was revealed that the planet's outer layer was deteriorating, leaving Drakulon unprotected against the blazing fury of its twin suns.

Her survival instinct stimulated by impending doom, Vampirella went against Drakulonium custom, killing the beasts of the planet and drinking their blood to survive. During her rebellion, explorers from Earth landed on Drakulon. The earthlings were barbaric compared to Drakulonium standards, and Vampirella was forced to attack them to protect herself. Realising that these Earthlings were filled with life-giving blood, and they would soon return to a planet full of blood-filled creatures, Vampirella stowed away on the spaceship and travelled to earth, where she became a vampire.

Or did she?

Vampirella later learned that she was the daughter of Lilith, the fist wife of Adam in the Garden of Eden. Strong-willed, Lilith refused Adam's advances, and God sent her to Hell, where she would fornicate with demons, and give birth to over 100 monsters a day. As punishment for refusing Adam, God would kill exactly 100 of Lilith's monstrous offspring every day, leaving some free to roam the earth. Lilith revealed to Vampirella that she was her favourite child, and was meant to act as Lilith's redemption. Vampirella learned that her true purpose was to destroy Lilith's other children, and end their reign of evil on Earth.

Or was it?

Before Vampirella was killed at the hands of Mistress Nyx, the villainess revealed that everything she knew was a lie.

Wizard

I haven't really kept up with Vampirella recently so her true origin is probably known by now. If it is please node it as I would be interested in reading 'bout it.