Xenon

Xenon was a powerful being who possessed a pathological hatred of Supergirl from every version of reality because one managed to imprison him at the dawn of time. Driven by vengeance, Xenon has hunted for all females who have bared the crest of Supergirl for thousands of years since being trapped. With the aid of his servant Fatalist, Xenon planned to collect alternate versions of Supergirl from different realities to kill them in order to destroy the seal that imprisons him and continue to murder all versions of his hated enemy.