Gatenzone, also known as Armored Captain Gatezone, is a major antagonist from the Kamen Rider Black RX film Sekai ni Kakeru. Within the narrative, he serves as a high-ranking officer of the Crisis Empire, a formidable interstellar force that serves as the primary enemy of the series protagonist. His specific designation is the commander of the Robot Unit, which consists of monstrous robotic soldiers. In addition to his field command, he is also tasked with managing the internal mechanics and systems of the Crisis Fortress, the empire's massive mobile headquarters.

As a character, Gatenzone is portrayed as a solitary figure with a distinctly nihilistic demeanor. He is often cynical and displays a sharp, critical wit, frequently making sarcastic remarks about the failures and shortcomings of his fellow commanders within the Crisis Empire. Despite his apparent disdain for his colleagues, he is completely loyal to the empire's goal of conquest. Gatenzone is depicted as possessing genius-level intelligence, being the mind responsible for the development and functioning of much of the empire's advanced technology. His age is reported to span thousands of years, with an implication that he was once trapped within the Demon World for a significant portion of that time.

In the story, Gatenzone engages the hero, Kamen Rider Black RX, on multiple occasions. As the leader of the Robot Unit, he coordinates attacks from his mechanical subordinates and personally confronts the Rider when the situation demands it. His role is that of a recurring obstacle, using both his strategic mind and his personal combat abilities to try and eliminate his foe. Unlike some of the more flamboyant or emotional villains of the Crisis Empire, Gatenzone operates with a cold, calculating efficiency, treating combat as a logical problem to be solved.

While no explicit key relationships are detailed, Gatenzone serves under General Jak, the leader of the Crisis Empire forces on Earth. He is a peer to other high-ranking commanders such as Dalom and Maribaron, though his cynical personality suggests a distant and possibly antagonistic relationship with them. His primary dynamic is his rivalry with Kamen Rider Black RX, whom he sees as a target to be eliminated to prove the superiority of his robotic forces.

In terms of development, Gatenzone remains a consistent antagonist throughout his appearances. His character arc culminates in a final, desperate battle against Black RX. In a last-ditch effort to destroy his enemy, he initiates a suicide attack, detaching his own head from his body and attempting to detonate his remaining form. However, the plan backfires; his own powerful laser beams are reflected back at him by Black RX, shattering his separated head and ending his millennia-long existence.

Gatenzone possesses a number of notable abilities that make him a dangerous adversary. He is considered the number one sniper in the Demon World and wields a double-barreled laser blaster with deadly accuracy. He can also fire potent energy beams from a single eye on his head. His most distinctive power is his ability to detach his head from his body while maintaining full control over both parts, allowing his body to continue moving and fighting independently. He also has the ability to disguise himself as a human. For transportation and combat, he rides a powerful motorcycle called the Storm Dagger, which is later upgraded with the Crisis Charger to become the even more potent Neo Storm Dagger. His body is highly durable, containing reinforcement cells that grant him resistance to the poisonous and acidic atmosphere of the Demon World, and he possesses a form of immortality that allows him to continue functioning even after being decapitated. His mechanical physiology classifies him as an inorganic lifeform. In the end, his final resort is a self-destruction mechanism, which he activates in a failed attempt to kill Kamen Rider BLACK RX.