Imperador Geldon is the primary antagonist and the main villain of the story. He originally serves as the military leader of a research mission from the planet Gailar. When the expedition's ship is forced to make an emergency landing on Earth, the crew enters a state of hibernation while awaiting rescue. After humans wake them through nuclear tests, Geldon consolidates his power by killing the original sovereign and proclaiming himself the new emperor of what becomes the Gailar Empire.

His personality is defined by tyranny, ambition, and ruthlessness. Geldon is a malevolent and dictatorial ruler who eliminates all opponents to his authority. He seeks to conquer Earth and establish his imperial dominion over the planet, showing no regard for the inhabitants or their world. His motivations are driven purely by a desire for power and expansion, as he views Earth as a territory with limitless potential for his new empire. He forces brilliant scientists like Professor Yan to create weapons of war, demonstrating his willingness to exploit anyone to achieve his goals.

In the narrative, Geldon serves as the commander who orders the relentless attacks on Earth. He commands his forces from a hidden base in the Arctic, dispatching bomber robots to assault cities, particularly in Japan. His primary objective regarding the main protagonists involves attempting to retrieve the advanced combat vessel Groizer X, which was built under his orders but stolen by Rita, the daughter of its creator, Professor Yan. Throughout the series, he consistently orders his subordinates to eliminate the pilots of Groizer X and bring the powerful machine back under his control.

Geldon maintains key relationships with several notable subordinates. He commands General Dagar, a military leader who secretly dreams of overthrowing him to become emperor himself. He also relies on Chief Golin, a scientist who develops the bomber robots used in the attacks on Earth. Additionally, the cruel Marshal Dógus, who possesses mechanical body parts, serves among his forces. His opposition to Professor Yan is central to the plot, as the scientist secretly opposes Geldons tyranny and ultimately sacrifices himself to help his daughter escape with the titular robot.

Regarding character development, Geldon remains the consistent driving force of evil throughout the series without undergoing a redemption arc or significant personal transformation. His role is firmly established as the tyrannical sovereign whose orders generate the conflict in each episode. His story concludes when the protagonists finally confront him directly. In the final episodes, frustrated by the repeated failures of his subordinates, Geldon decides to take matters into his own hands and personally engages in battle against Groizer X. He is ultimately destroyed, bringing an end to his reign and the threat of the Gailar Empire.

Regarding notable abilities, the available information focuses on his role as a commander and ruler rather than any personal combat skills or special powers. His strength lies in his authority over the Gailar military forces, his strategic positioning as the emperor, and his control over the empires resources and technology, including the development of destructive bomber robots. His abilities are those of a dictatorial leader and military commander rather than a physical combatant.