Lilith, Reaper of Souls
Lilith hates humans. However, she started as one herself. Farther back than she even remembers anymore, she was one of the first humans. They were originally immortals who lived in a utopia under the shadow of the World Tree on Earth. Their lives were mostly free of care but she was rebellious of others around her that sought to control and force her into subservience. She was eventually ostracized and banished after she attempted to unlock the forbidden secrets of the World Tree. For her transgression, the World Tree was removed from Earth removing immortality from all humans. It is unclear who removed the World Tree, created its prohibition or even created humans in the first place.
Regardless, she had already accessed forbidden knowledge of life and death from the world tree and Azrael, the Angel of Death was dispatched to eliminate her. In these ancient times, angels and demons were common knowledge and were not separated from the human world until after the World Tree was removed. Lilith contacted the demon, Lucifer, and offered some of her knowledge to him, particularly how to kill angels, in exchange for power. The demons took her in and transformed her into one of them; she took on the form of a succubus. She became the punisher and tormentor of human lust and perversion. Of note, she didn’t divulge all her knowledge to the demons, only enough to accomplish her goals.
Azrael, Angel of Death
Unwavering, Azrael pursued her for eons to finish his mission but Lilith was cunning and always managed to stay ahead of him. An eternal war between angels and demons raged and yet still his edict remained. Eventually, he did catch up to her but it was then she sprung a trap centuries in the making and was able to defeat him. Here she revealed her true knowledge of life, death, angels and demons. She destroyed his form and absorbed it transforming herself into a new entity. She became the incarnation of death itself and proclaimed herself the absolute authority over life and death, siding with neither the celestials or infernals.
At this point, she seemed to disappear from history and presumably took on the role of death itself. Ironically, it also seems she was now under the direction of whatever eternal force created everything in the first place as she executed the duties of her new role.
But there was always a deep-seated hate for humans in her very core. She would gladly commit genocide on the entire human species, but obviously has not. She was strictly forbidden to and she simply lacked the actual power to do so. This didn’t stop her from trying.
The Unspeakable Entity
Eventually, she learned of the Unspeakable Entity and his whispered promises of untold power. He stoked her lust for power and validated the deep hate, anger and resentment burning within her. Both gleefully colluded while planning their inevitable betrayal of each other. He divulged the secrets of the Singularity and how to break the impossibility of reaching the Vanishing Point. Details are unknown but it certainly involved actually moving a supermassive black hole and traversing two, three and fourth-dimensional planes simultaneously. Some of this she accomplished on her own and some of it she enlisted the aid of other unwitting incarnations.
Suffice it to say, she eventually succeeded in her quest to arrive at the Vanishing Point and access its power for herself. Of course, this was the one lie she did believe and instead of obtaining it, she was drained when the Singularity ruptured and plunged the multiverse into a crash course with oblivion.