Leon Cromwell arrived in the Central World roughly 300 years ago as a child human from another world, alongside his close companion Chloe Aubert. Chloe vanished shortly after their arrival through dimensional distortion, igniting his lifelong quest to reunite with her, a pursuit defining his existence. His appearance features long platinum-blonde hair, pale skin, narrow blue eyes, and strikingly androgynous features often leading to initial misidentification as female. Despite this youthful presentation, he is centuries old, typically dressed in a black overcoat over garments resembling priestly robes with gray and yellow patterns. Outwardly, Leon presents as cold, prideful, and calculative, especially when dealing with powerful figures like Guy Crimson or Velzard. This demeanor stems from inherent difficulty expressing emotion, frequently causing misunderstandings. Beneath this lies a capacity for kindness overshadowed by his singular fixation on Chloe; situations involving her trigger hotheaded, overprotective behavior. His obsession drove ethically questionable actions, including spreading incomplete summoning rituals that pulled otherworlder children like Shizue Izawa to the Central World. He saved Shizue by binding the fire spirit Ifrit to her, an act perceived as cruel due to his detached manner. His history began upon arrival. After Chloe's disappearance, he contracted an Elemental of Light in Ramiris's labyrinth, gaining the title "Hero" and alias "Platinum Saber." Approximately 200 years later, after a lethal victory over Demon Lord Kazaream, he claimed the title for himself, seizing Kazaream's castle and council seat. This transition altered his alias to "Platinum Devil" and established his role within the Octagram coalition. His summoning experiments targeting Chloe inadvertently summoned Shizue from wartime Tokyo. Though Ifrit sustained her, mutual mistrust and Shizue's trauma eroded their relationship, culminating in Leon abandoning his castle upon a Masked Hero's approach – later revealed as Chloe. Leon ranks among the most formidable beings. His initial Hero status evolved into True Demon Lord capabilities, later advancing to Demigod physiology after core reconstruction. He wields the Ultimate Skill "King of Purity: Metatron," specializing in light-based attacks operating at atomic or spiritual levels, including near-light-speed sword thrusts and continent-scale destruction. Signature techniques are "Holy Breakdown" for inescapable annihilation within barriers and "Sacred Tetrahedron Demon Sealing Barrier" for high-level containment. Additional proficiencies encompass spatial travel, flight, multi-layered barriers, and resistance to most magic or lower-tier abilities via Ultimate Skill dominance, with combat endurance permitting day-long engagements. Relationships center on Chloe Aubert as his emotional anchor, driving centuries of dedication. Interactions with Rimuru Tempest began antagonistically due to Shizue's history but transitioned to cooperation after misunderstandings regarding her care were resolved, leading him to entrust Chloe's safety to Rimuru. Guy Crimson maintains persistent, unwelcome romantic advances, causing irritation. Ramiris provokes discomfort through childhood references, while Elmesia El Ru Sarion considers him excessively taciturn. He rules El Dorado, a continent-sized territory bordering the demon world, sheltering orphans and outcasts, demonstrating unexpected administrative compassion despite initial motivations solely focused on locating Chloe. Current activities integrate governance of El Dorado with ongoing strategic alliances. Following Chloe's retrieval and temporal stabilization, he participates in broader conflicts, leveraging his evolved Ultimate Skill "King of Radiance: Surya" and status among the Octagram's key figures.