Léon Cromwell originated as a human summoned from another world to the Central World roughly 300 years ago, arriving alongside his childhood companion Chloe Aubert. Chloe vanished immediately after their arrival, igniting his centuries-long quest to find her. To aid this search, he contracted with an elemental of light, gaining recognition as a Chosen Hero during his early travels, a period when he also formed a friendship with Elmesia El Ru Sarion. Approximately 200 years ago, Léon engaged in a life-or-death battle against the Demon Lord Kazalim and emerged victorious. Claiming the defeated Demon Lord's title for himself, he assumed Kazalim's seat as the seventh member of the Octagram council. His aliases evolved to Platinum Devil and Platinum Saber. He established and governs the territory of El Dorado, bordering the demon world to the south, creating within it a sanctuary for orphans and societal outcasts, many gathered by his own hand. Driven relentlessly by his search for Chloe, Léon systematically disseminated incomplete summoning rituals across human nations, collaborating with merchants and clandestine groups. This resulted in numerous otherworlder children, including Shizue Izawa summoned during the Tokyo firebombings of World War II, being brought against their will. Recognizing Shizue's affinity for fire magic, he bound the fire spirit Ifrit to her as protection and a potential vessel. However, Léon's emotionally distant nature, Shizue's traumatic adjustment, and Ifrit's misinterpretations led to a tragic deterioration of their relationship, culminating in abandonment when Léon left Shizue with the Masked Hero. Physically, Léon possesses long platinum-gold hair, piercing blue eyes, and an androgynously beautiful face often mistaken for feminine. He retains the appearance of a young adult despite being over three centuries old. His personality typically presents as cold, rational, and emotionally restrained, frequently causing misunderstandings about his motives. This detached exterior masks a fundamentally kind nature, though his singular focus on Chloe drives him to commit morally questionable acts, including ritual manipulation. His demeanor shifts dramatically regarding Chloe, revealing intense protectiveness and impulsiveness. He maintains complex dynamics with powerful entities, respecting Guy Crimson as an equal while repeatedly rejecting romantic advances, and sharing a distinct rivalry with Velzard. Léon's combat abilities are formidable, centered on masterful swordsmanship that earned him the epithet Platinum Saber. He wields a legendary holy sword and commands potent magic. His signature powers include the ultimate angelic skill "King of Purity" (Metatron), enabling target eradication with pure energy and holy magic like "Spirit Particle Collapse," later evolving into "King of Radiance" (Surya). He exercises meticulous control over these destructive capabilities, executing wide-area assaults while minimizing collateral damage. Key developments include his participation in the Demon Lords' Walpurgis banquet, where he learned Shizue's final wishes through Rimuru Tempest. Combined with Rimuru's ascension to Demon Lord status and intervention halting otherworlder summonings, this led Léon to abandon his proxy-summoning schemes. During later confrontations within the Holy Empire of Lubelios, he discerned Archbishop Granbell Rosso's manipulations designed to provoke conflict between him and Rimuru. Choosing to trust Rimuru instead, Léon achieved a long-awaited reunion with Chloe. Though initially separated again by her time-displacement abilities, they ultimately reconciled after overcoming numerous obstacles, during which Chloe revealed the full scope of her temporal experiences. Persistent traits include his tendency toward isolation, shouldering burdens alone, and concealing true intentions, which allies like Elmesia interpret as excessive silence and stubbornness. Ramiris, acquainted with him since childhood, often teases him, causing noticeable discomfort. His actions remain consistently motivated by unwavering devotion to Chloe, accepting that others may never understand his choices.