King is the human form adopted by the Caucasus Beetle Undead, who holds the rank of Category King of Spades within the Undead hierarchy. In his human guise, he appears as a teenage boy, though his true Undead form is a powerful, gold-colored beetle warrior. He refers to himself simply as King, a name he chose to signify his status as the strongest being.

The personality of King is distinctly childish, cruel, and remarkably petty for a creature of his power. He takes great pleasure in causing trouble for others, bullying, and observing the resulting suffering. He has a particularly malicious hobby of using his mobile phone to photograph people in moments of distress or sadness, which he then uploads to his personal website for his own amusement. He views humans as little more than playthings and feels no guilt or remorse for his actions. Unlike other high-ranking Undead who may have a specific purpose in the Battle Fight, King has no interest in the ancient ritual or any mission. His sole motivation is to create chaos and make a mess of everything simply because he finds it entertaining and is bored with the existing order.

Within the story of Kamen Rider Blade, King acts as a significant disruptive force who manipulates events from the shadows. He is first seen controlling the Scarab Undead, a subordinate he commands to obey him and use its time-stopping abilities on his behalf. His primary goal is to destabilize the fragile peace by targeting the Riders and, most crucially, Hajime Aikawa, the Joker Undead. Knowing Hajime's true identity, King steals his Rouze Cards, intending to strip away his control and force him to revert to his berserker Joker form. He then gives the stolen deck to Mutsuki Kamijo, the user of the Leangle system, further stirring up conflict to enjoy the resulting "mess".

King's key relationships are defined by his antagonistic and manipulative nature. He serves as a direct foe to Kazuma Kenzaki, Kamen Rider Blade, and the other Riders. His most significant act is his interference with Hajime Aikawa, deliberately triggering the Joker's dangerous transformation. He also has a master-servant relationship with the Scarab Undead, whom he uses as a tool for his schemes. Despite his power and scheming, his development follows a classic arc of a villain brought down by his own arrogance. He is confronted by Kenzaki, who, even after having all his Rouze Cards taken, refuses to give up. In a desperate final battle, Kenzaki shatters King's legendary shield and defeats him, sealing the Caucasus Beetle Undead within a Rouze Card. Even in defeat, King shows his spiteful nature, sarcastically warning Kenzaki to be careful not to be dominated by him like Leangle was, though this threat never comes to pass.

As a Category King, his notable abilities are immense. In combat, he wields a bifurcated greatsword called the All-Over and a virtually indestructible shield known as the Solid Shield, which can withstand impacts of up to 150 tons. One of his most formidable traits is his ability to summon this shield instantly, even while in his human form, to block any attack automatically. He also possesses potent telekinesis, which he uses to move objects, create invisible barriers, and send people flying with a gesture. Furthermore, he can generate powerful gusts of wind from his hands, referred to as a Typhoon Blast, to knock back his enemies. His most strategic power is his ability to control the minds of other Undead, which he uses to command the Scarab Undead to stop time for his benefit. His sealing by Blade later provides the protagonist with the means to assume his own King Form, a testament to the power of the card he represents.