>>41027160The origins of Zekrom and Reshiram are told in legends, as they were once a single powerful Dragon Pokémon used by twin heroes in order to create the Unova region. But the brothers each sought something different in life—truth for the older brother and ideals for the younger—and they began to argue, then fight, over whose side was right. The single dragon, in response, split into two Pokémon: Reshiram, who sided with the older twin, and Zekrom, who sided with the younger twin.
The two dragons were equally matched as they battled and neither conquered the other. As a result, the brothers set aside their differences and equally declared that there was no right side, either. But the sons of the heroes resumed the fight, and Reshiram and Zekrom destroyed the region with their fire and lightning powers. They subsequently disappeared afterward.