Sosai X, also known as Leader X, originated from the planet Selector (or Selectol/Select Star) in the Andromeda Nebula, approximately two million light years from Earth. Sent by his superiors, X arrived on Earth a thousand years before the main series events, lying dormant until initiating operations to conquer the planet. His initial mission exploited Earth's strategic location between Proxima and Andromeda to forge a weapon for an interstellar war against the rival Fueless Star, leveraging the Sun's properties. To achieve this, X transformed a small criminal mafia into the global terrorist organization Galactor, incorporating various wicked groups worldwide and using Earth's resources. X typically manifested as a vague, shadowy figure with a purple hue, blue beak-like details, red markings, and piercing yellow eyes. He communicated through an artificial intelligence interface displayed on a circular yellow screen surrounded by an orange, cloudy substance, resembling a giant eye. This screen design evolved across the series, becoming smaller and more colorful in later seasons. X's true physical form was later revealed as a biological super-computer composed of machinery and energy tubes, created by Selector. After apparent destruction, a fragment regenerated into a new, more formidable pyramid-like structure known as Sosai Z (or Leader Z), characterized by greater ruthlessness. Personality-wise, X exhibited cruelty, manipulation, and arrogance, viewing humans as expendable tools. He demonstrated no empathy, evidenced by massacring a cruise ship of innocents and kidnapping a young girl molded into Gel Sadora. He demanded absolute loyalty from subordinates but readily disposed of those who failed or outlived their usefulness, including Berg Katse and Gel Sadora. His arrogance led him to dismiss Earth's inhabitants as incapable of defeating him, though this was challenged by the Science Ninja Team. Learning of Selector's destruction years prior shifted X's motives from conquest to pure spite-driven annihilation of Earth. In the original series, X orchestrated Galactor's activities through his second-in-command, Berg Katse—a mutant fusion of fraternal twins engineered by X. Discovering Selector's destruction, X abandoned colonization and initiated the "Black Hole Operation," aiming to implant a black hole in Earth's core to destroy the planet. Katse, disillusioned, committed suicide. X was seemingly defeated when the Science Ninja Team destroyed his mechanism, though he survived, later attacking a cruise ship to abduct a girl groomed as Katse's successor, Gel Sadora. When Sadora rebelled upon learning her origins, X ordered her execution. He was again presumed destroyed in an assault on his base. A remnant of X's body regenerated into Sosai Z in the sequel series *Gatchaman II* and *Gatchaman Fighter*. Rebuilding Galactor with Count Egobossler, Z launched the "Solar Shift Plan" to harness the Sun's energy for destruction, followed by "Operation Poison Apple," which aimed to devastate Earth using an antimatter asteroid. After Egobossler outlived his usefulness, Z killed him. Z's final defeat occurred when the Science Ninja Team destroyed his pyramid form with the Gatchaspartan; his ultimate fate remained ambiguous as the pyramid imploded into a black hole. English adaptations significantly altered X's character. *Battle of the Planets* (1978) depicted him as "The Great Spirit" or "Luminous One," ruler of the dying planet Spectra seeking to plunder Earth's resources. *G-Force: Guardians of Space* (1987) reduced him to "Computor," a mere consultant to Galactor, while *Eagle Riders* (1996) renamed him "Cybercon," retaining his malevolent traits. The OVA adaptation by Harmony Gold dubbed him "Lord Zortek." Development notes reveal X was initially conceived as an AI construct created by Berg Katse to manipulate Galactor members, with plans to reveal this in the series finale. This concept was abandoned due to creative disagreements and the challenges of visually conveying a sentient computer in animation. The revised backstory established X as an alien entity, though elements of his AI origins persisted in sequels, where he was depicted as a self-regenerating bio-computer.