Lady Demon came about when Lady Death realizes that her life in hell was all a plan by Lucifer who had controlled and directed her like a puppet. The journey of self realization was so traumatic her demonic persona came to a life of its own and Lady Death became Lady Demon.
The demonic being cast Purgatori out of Hell and back to Earth, much to her torment and dismay. Lady Demon became Lucifer's consort for a short time until Marion, Lady Death's mother, came to her making Lady Death come to her senses. Lady Death absorbed her mother's angelic powers to return to battle Lucifer. In the end Lady Death casts Lucifer through the Nexus and into the gates of heaven.
As she accustoms to being Lady Demon she travels Hell to see its wonders. She is accompanied by Lucifer, or is saved by him from time to time; like when Lady Demon found Spear of Destiny in Hell and tried to claim it as her own. She was stopped by Lucifer as touching it would have killed her. One time Matthias tries to trick Lady Demon to release him but she sees through his deception and lets him rot in his chains.
Later Lady Demon came to exist as a being on her own with dark intent. She sought out Lady Death to combine with her once more, only to fail. Lady Demon escaped Lady Death's wrath by merging with a mortal woman by the name of Cheryl Montessori. Cheryl was a co-op agent. After the merging with the mortal; Lady Demon was able to escape hell. Cheryl managed to survive along with Lady Demon and they both struggled for the body's control.
After the Armageddon Lady Demon is recreated still fighting to control the body she inhabits. She woke as Cheryl beside a body, and soon after that government soldiers from ETC stormed in her door. Lady Demon took over and fled that place killing as many men she could. She again turns back to Cheryl to rest. Lady Demon has a weakness though, when she merged with a mortal, she made herself vulnerable; she was gunned down by the mafia on the street and then taken captive. The warehouse where she was kept in was raided by ETC, which only served as a distraction to escape her bonds to Lady Demon. Cheryl looks a way to get both the Mob and ETC off her back.
Lady Demon and Cheryl had a final fight over the body, Cheryl agreed to release Lady Demon freely, and let her kill as many enemies she wants. They then go to see Vittorio, old love of Cheryl. But Vittorio knows Lady Demon is inside Cheryl and calls her out, he then proposes that she'd work for him and he could arrange an operation that would give her total control over the body. While Lady Demon and Vittorio are discussing the details, ETC attacks the restaurant they are in. Lady Demon fights both sides and comes out as victor. But Cheryl has decides to rid herself of Lady Demon, she threatens to kill herself (that would also kill Lady Demon) if she don't leave her body. Lady Demon curses Cheryl and leaves her body, she starts to look for a new body to inhabit, otherwise she would be pulled back to Hell. She finds one woman who has killed her husband and then herself. This body suits Lady Demon better than the last one.