Nocturna is Natalia Knight, a Gotham City criminal and enemy to Batman. Due to an accident while studying astronomy, her skin turned white and became vulnerable to light. Her original partner and adoptive brother was the criminal Night-Slayer.
After the Crisis on Infinite Earths, a similar character was re-envisioned as occultist Natalia Mitternich, who was hinted at becoming the new Nocturna, though she never appeared after her original storyline.
The New 52 reboot presented a combination of the former characters and Nocturna is Natalia Mitternacht, a socialite and nemesis to Batwoman, showing vampire-like abilities. She also serves as a member of the Secret Society of Super-Villains.