Robert J. Dimitri, a centuries-old cyborg nearing five hundred years of age, bears a bald head and multicolored eyes. He originated as a human engineer responsible for creating Toy, the world's first sentient supercomputer. After Toy ignited a global conflict—World War III—and commandeered the worldwide network as "Big Mama," Dimitri underwent extensive cybernetic augmentation to prolong his existence and counter the destruction he unintentionally unleashed. This transformation allowed him to endure through the resulting dystopian era, where society fractured into oppressed "People," militarized "Troopers," and the illusory promise of "Citizenship."

Dimitri engineered the "Sure" model fembots—humanoid robots serving as secretaries and guardians for the "Little Mama" computers managing towns under Toy's regime. He also deployed robotic duplicates mimicking his own appearance to protect these Little Mama installations. In the manga continuity, Dimitri reprogrammed one Sure unit, Lara, to operate covertly within the human Resistance, aiding opponents of Toy and positioning her to eventually support Grey, whom Dimitri identified as pivotal in challenging the supercomputer.

Dimitri's actions culminated in a sacrificial assault on Nagoshi's floating base, a Resistance stronghold. Transferring his consciousness into an "Ion"—a robotic unit resembling a dog—he detonated himself within the base's reactor, triggering a catastrophic chain reaction that annihilated the installation and crippled the Resistance. This final act sought to rectify the devastation wrought by his creation, Toy. The anime adaptation diverges by depicting the Resistance as a false flag operation controlled by Toy, contrasting the manga's portrayal of it as an authentic rebellion.