King Vega rules the unstable planet Vega, destabilized by rampant Vegatron exploitation—a potent radioactive material. This environmental catastrophe drives his expansionist quest for a new habitable world. He targets peaceful Fleed among neighboring planets, approaching King Fleed under deceptive benevolence to arrange Princess Rubina's engagement to Crown Prince Duke Fleed. After securing trust, he unleashes a devastating surprise assault: deploying massive fleets, colossal robots, and Vegatron bombs that annihilate Fleed's armies, cities, and royal family.

The Vegatron bombardment ironically renders Fleed a radioactive wasteland, voiding his colonization objective. His forces also fail to capture Grendizer—Fleed's god of war in robotic form—as Duke Fleed escapes with it to Earth. Vega redirects his armies toward Earth, confirming Duke's presence through initial raids. He commands remotely from Vega, tasking generals like Gandal and Blaki with direct confrontations. When Vega's environment fully collapses, he relocates to the Skull Moon Base on the Moon's dark side, personally intensifying Earth's invasion.

Rubina discovers Fleed's recovery and Duke's survival, traveling to Earth to warn him. One of Vega's generals exploits her presence to ambush Duke, but Rubina dies shielding him from an attack. Her death galvanizes Duke Fleed's resolve against him.

In the conflict's climax, Vega orders Earth's full-scale assault. To prevent retreat, he destroys the Skull Moon Base, commanding the offensive from a colossal mother ship. The campaign culminates in a decisive battle where his mother ship is obliterated, killing him.

Ruthless and cunning, Vega employs deception and overwhelming force to dominate. His leadership sacrifices subordinates and resources without hesitation. A tragic past reveals he was once a Vega Empire scientist, betrayed and exiled by colleagues, forging bitter vengeance against his former empire and beyond.