Rudolf originated as a renowned human hero wielding immense magical talent, fighting alongside his sister Maria to protect humanity. Maria's death during a conflict became the pivotal catalyst: consumed by grief and rage, he abandoned heroism to pursue ultimate power through forbidden dark magic. This quest transformed him into the Demon King, complete with a demon army and fortress.

As Demon King, Rudolf commands vast magical power and exhibits sharp intelligence, favoring psychological manipulation over direct combat. His actions remain fueled by Maria's loss, cementing his conviction that absolute control prevents tragedy. He maintains a complex dynamic with Alba, the current hero, recognizing Alba's potential. Rudolf tests and manipulates Alba through cryptic guidance and calculated provocations, viewing him as both a successor and a reflection of his own former ideals.

Flashbacks depict Rudolf's past idealism and protective nature toward Maria. Her death shattered his worldview, directly triggering his descent. Lingering traces of his former self surface through his interest in Alba's growth. Magically, Rudolf specializes in potent dark spells, barriers, curses, teleportation, energy projection, and near-impenetrable defenses. His power consistently dwarfs others, requiring extraordinary measures to challenge him.

All Rudolf's actions stem from his trauma-forged philosophy: the world’s cruelty demands absolute power for security. He deems the hero system flawed and seeks to force Alba to confront this reality, potentially embracing power as Rudolf did. He orchestrates conflicts, tests heroes, and unveils hidden truths about the world’s mechanics. Rudolf holds deep knowledge of ancient magic, the demon realm, and the systems governing heroes and demons, remaining an enigmatic figure defined by his past tragedy.