He is described to be a once heroic Ultraman, named; Ultraman Zoul, but he then turned evil, predating Ultraman Belial.
Along the way, he would learn about Project Ultraman in the highly-guarded BASE 64, and through his encounters with Millennium, he would eventually have a change of heart that would have resulted in him siding with them (alongside Ultraman Elite) to stop S' plans from coming to fruition.
