Goa, an alien entity resembling a lizard in his true form, pursues the conquest of Earth. He typically adopts the guise of a gentleman in an elegant suit, presenting as human to advance his plans. His invasion begins by transporting the Murakami family to a prehistoric jungle, where he destroys the giant dinosaur Agon as a display of power and a warning to compel humanity's surrender.

To wreak havoc, particularly in the greater Tokyo area, Goa unleashes various dinosaur-like monsters; these creatures often require multiple episodes to defeat, driving serialized story arcs. He utilizes proxy agents called Modoki Men (Lugo Men in English adaptations), faceless ninja-like entities that dissolve into oozing slime upon death. These agents conduct espionage, kidnappings, and other tasks, including the abduction of Tomoko Murakami, which becomes a significant subplot.

Beyond simple conquest, Goa claims a motivation to create a world governed solely by children, though the implications of this vision remain ambiguous. His operations occasionally display complexity, such as in the manga episode "The Two Yukies," where an alien impersonating a human girl evokes greater sympathy than her human counterpart.

Goa faces opposition from Earth's creator residing beneath the planet's surface. This entity generates golden protector beings to counter Goa's threats, and their conflict forms the narrative core across all adaptations. In the 1993 OVA series retelling, Goa's role and objectives remain consistent with the source material. The character also appears in the video game *Astro Boy: Omega Factor*, confirming his place within Osamu Tezuka's broader narrative universe.