Sosai X, also known as Leader X, originates from the planet Selectol (alternatively Selector or Select Star) in the Andromeda Nebula. Sent to Earth by his superiors, his initial mission was planetary conquest for colonization. To achieve this, he transformed a small criminal group into the global terrorist organization Galactor, incorporating other malicious entities worldwide. A key act involved forcibly fusing fraternal twins within their mother's womb, creating the mutant Berg Katse to serve as his primary subordinate and Galactor's public face. Throughout most of the original series, Sosai X remained hidden, communicating via an artificial intelligence interface depicted as a purple-hued shadow with a beak-like blue detail, red markings, and yellow eyes, often displayed within a circular screen resembling a giant eye. This enigmatic form reinforced his mystique. Early concepts envisioned him as Katse's supercomputer, but this was discarded for the alien origin. His personality exhibited extreme cruelty, arrogance, manipulation, and a complete lack of empathy. He readily disposed of failed or useless subordinates, exemplified by abandoning Katse upon learning of Selectol's destruction years prior due to an interstellar war with planet Proxima. Selectol's destruction shifted Sosai X's objectives. Abandoning colonization, he instead sought to destroy Earth by creating an artificial black hole at its core. The Science Ninja Team thwarted this plan, leading to Katse's suicide and Sosai X's apparent destruction. However, he survived. Returning roughly two years later in "Gatchaman II," Sosai X sought vengeance against the Science Ninja Team and Proxima. His re-emergence began with an attack on a cruise ship, killing nearly all passengers and kidnapping a young girl possessing special chromosomes. He forcibly mutated this child into Gel Sadora (or Gel Sadra), a new androgynous commander for the rebuilt Galactor, intended to replace Katse. During this period, his communication form appeared more colorful and utilized a smaller device. His primary scheme, the "Solar Shift Plan," aimed to harness Earth's sun as a weapon against Proxima. He operated with increased ruthlessness, viewing Earth solely as a tool for revenge. Despite Gel Sadora discovering her origins and rebelling, Sosai X ordered her execution. Although seemingly destroyed again at the end of "Gatchaman II," a minuscule fragment of Sosai X survived. This remnant regenerated over time, rebuilding itself using an abandoned shipyard's remains and emerging as the more powerful Sosai Z in "Gatchaman Fighter." Resembling a massive, menacing structure, Sosai Z recruited dictator Count Egobossler to rebuild Galactor and initiated "Operation Poison Apple," a plan to devastate Earth using an antimatter asteroid. Demonstrating his consistent betrayal, Sosai Z killed Egobossler once deemed expendable. Sosai Z's reign ended when the Science Ninja Team destroyed his pyramid form, seemingly sacrificing themselves to eliminate him permanently. His ultimate fate after the pyramid imploded into a black hole remains ambiguous.