Diablo, born as Noir, stands among the seven primordial daemons as the ancient entity known as the "Primordial Black." Existing long before the rise of civilizations, he once roamed without purpose, his innate power rendering ambition unnecessary. This indifference shattered upon encountering Shizue Izawa, a human whose Anti-Magic Mask defied his might, igniting his obsession with its origin. His focus shifted to Rimuru Tempest, whom he deemed central to unraveling the world’s hidden truths—a conviction solidified after years of failed summoning attempts culminated in his emergence during Falmuth’s invasion. Offering two subordinate demons as sacrificial offerings to secure Rimuru’s trust, Noir ascended to Daemon Lord status upon receiving the name "Diablo," adopting a refined butler’s guise. His striking visage—sleek black hair streaked with crimson and gold, piercing golden eyes with crimson pupils framed by black sclerae—exudes regal menace. Bound by fanatical loyalty, Diablo serves Rimuru with meticulous precision, twisting command ambiguities to advance his own enigmatic goals. He orchestrates schemes through the Black Numbers, an elite force led by fellow primordial daemons Testarossa, Ultima, and Carrera, dismantling adversaries of the Tempest regime with calculated ruthlessness. His combat prowess transcends conventional limits: resistances negate all attack forms, while abilities like "Tempter" enslave minds and souls, and "Despair Time" traps foes in illusionary domains annihilated by "End of the World." With an energy potential of 6,666,666 EP and his evolution into a Demon King, he reigns as Rimuru’s most formidable ally. Interactions reveal layered dynamics—respectful rivalry with Rimuru’s confidants like Shion, tense parity with the primordial Guy Crimson, and disdainful intrigue toward his descendant Beretta. Once a capricious force of ennui, he now thrives as a master strategist, channeling ancient whimsy into unwavering service. Beyond battlefields, he manipulates politics, harvests souls for Rimuru’s ascension, and navigates cross-dimensional alliances, blending charm and terror to shape empires. Whether in alternate timelines or collaborative conflicts, Diablo’s legacy endures as a primordial enigma reborn through devotion to his sovereign’s destiny.