Upside Down Man was created by James Tynion IV and Alvaro Martinez.
The Upside Down Man was one of the first beings birthed from magic. He developed alongside the being that would become Hecate as her shadow self. She didn't like the darkness she felt from him, so she barred him from Earth. However, when humans turned on her for her power, her hate pierced the veil and stole some of his and his people's power. With that, she infected the magicworld with chaos and set the stage for his inevitable return.