Sir Nylon acts as Duke Duralumin's loyal henchman, assisting the Duke's schemes to reveal Princess Sapphire's true gender and seize control of Silverland. He is physically tall and lanky, featuring a distinctive long, tube-shaped nose and often dressed in foppish green attire, aligning with Tezuka's recurring "large nose" character design. As the Duke's primary enforcer, he handles physical tasks including kidnapping and intimidation. However, his consistent incompetence leads to frequent failures, earning him verbal and physical abuse from the Duke. Although relatively skilled with a sword, he is consistently outmatched by Sapphire in combat.

In the original 1953 manga, Sir Nylon's treachery peaks when he assassinates Duke Duralumin during a coup, driven to near-insanity by persistent mistreatment. After the assassination, he proclaims himself ruler and allies with the invading forces of Mr. X, only to be betrayed and treated as a buffoon. His demise comes when Mr. X causes Silverland Castle to collapse, crushing him to death.

The 1960s manga adaptation alters his arc: Sir Nylon mortally wounds both Sapphire and Plastic (Duke Duralumin's son) during an assassination attempt. This act directly triggers Duke Duralumin's suicide as atonement. This version retains his persistent antagonism while amplifying his impact through more consequential violence.

Across all media, Sir Nylon functions as a secondary antagonist whose bumbling nature provides comedic relief, though his actions escalate to drive critical plot points during climaxes involving political upheaval or invasion. His character lacks significant backstory or development beyond his minion role, with no spin-offs expanding his origins. His fate remains tied to the collapse of Silverland's established order.