Duke Duralumon, alternately spelled Duralumin or Jeralmin in certain adaptations, functions as a recurring primary antagonist in various iterations of the story. A royal relative, he orchestrates schemes to install his son, Plastic, on Silverland’s throne, exploiting the kingdom’s male-preference succession laws to delegitimize Princess Sapphire’s claim. His ambitions are driven by a hunger for political dominance, particularly his fear that the reigning king’s progressive reforms would erode his power. Aligned with accomplices such as Baron Nylon, he deploys diverse strategies, from public character assassinations to covert alliances with supernatural forces like Satan and the fascist X-Union leader Mr. X.

Physically, he is portrayed as short, balding, and portly, with a signature mustache and hairstyle. Though capable of fleeting paternal gestures toward Plastic, his parenting remains manipulative, marked by condescension toward his son’s capabilities. This dynamic fractures across adaptations: the 50s manga sees Plastic defying him after maturing, while the 60s version concludes with the Duke’s suicide following Nylon’s fatal attack on both Plastic and Sapphire. His partnership with Nylon crumbles under sustained mistreatment, culminating in Nylon’s betrayal and assassination of the Duke during an anime-depicted coup.

Narratively, he transitions from a farcical, inept foe to a tool of darker powers like Mr. X, who weaponizes his aspirations for conquest. His demise typically stems from overconfidence and failed control over allies, positioning him as a bridge between localized political strife and Silverland’s existential crises. His name, inspired by the alloy duralumin, underscores themes of adaptable durability and shifting loyalties.