Doppler, often addressed as Chancellor Doppler, is the primary antagonist of the series. He originally appears as an individual who, after the destruction of the first exploration ships heading to the tenth planet Promete, takes his own vessel to the planet and declares himself its Chancellor. Operating from this position, he constructs a vast military force using Promete's resources, creating an army more powerful than that of Earth. His central motivation is a possessive and obsessive belief that only he is entitled to the planet Promete, and he forbids anyone else from approaching it, threatening destruction to any who defy his command.

In terms of personality, Doppler exhibits traits of an egomaniacal and dictatorial ruler. His behavior is described as driven by an insane conviction of his own exclusive right to the planet. He styles himself as a Führer-like figure, often dressing in a manner reminiscent of a dictator and commanding soldiers who wear uniforms and bear names modeled after Nazi officers. This design choice visually reinforces his role as a ruthless and tyrannical force within the narrative.

Doppler's role in the story is to serve as the central obstacle to Earth's goal of colonizing Promete to escape its resource-depleted homeworld. To counter Earth's efforts, he systematically attacks and destroys all of the massive combat robots built by Earth's governments, succeeding in every case except for the title robot, Danguard Ace. His forces directly oppose the young pilot Takuma Ichimonji and the crew of the Danguard base, making him the primary source of conflict that the protagonists must overcome.

Key relationships in Doppler's story are defined by opposition and control. Directly opposing him is Captain Dan, a mysterious masked man who was once under Doppler's mind control but broke free and now uses his skills to defend the Danguard project. The protagonist, Takuma Ichimonji, is the son of the man who betrayed the initial Promete exploration team; Takuma pilots Danguard Ace specifically to restore his family's honor by fighting Doppler's forces. Doppler's relationship with his own army is one of absolute command, as he uses his vast resources to deploy a relentless series of military forces, including giant robots called mecha satans, to destroy his enemies.

Regarding development, Doppler remains a consistent and formidable antagonist throughout the series. His backstory involves leaving Earth for Promete after the initial exploration mission fails, establishing his base of power from which he launches his campaign. While his personal history is not deeply explored, his actions directly shape the plot and the motivations of the main characters. He is the architect of the circumstances that led to Captain Dan's enslavement and the perceived betrayal by Takuma's father, cementing him as the source of the series' central conflicts.

Notable abilities of Doppler are not centered on physical combat but on strategic and technological dominance. His primary ability is his vast wealth and intellect, which he uses to amass a formidable military force, including a fleet of warships and an army of powerful robots. He is also capable of employing advanced mind-control technology, which he uses to subjugate captive astronauts like Captain Dan and force them to serve him as enslaved workers on Promete. This combination of resources and technological control makes him a powerful and persistent threat to Earth and the heroes of Danguard Ace.