Professor Amagi, also known by his criminal alias Dr. Machinegal, is a brilliant and eccentric scientist in the anime Moldiver. He is a senior figure in the science world of this future version of Tokyo: the developer of the theory behind the towering mega-structures known as complexes, a science adviser to the major corporation ZIC, and the former university teacher and mentor of the inventor Hiroshi Ozora. In his student days, Hiroshi researched super-dimensional armor under Amagi's guidance. Amagi had developed the theoretical basis for this armor, which uses special particles called pseudo-molecules to allow a wearer to control and cancel out physical limits, but he sealed the project because no known substance on Earth could act as the catalyst needed to anchor the pseudo-molecules to a human body. Hiroshi later continued the work on his own after discovering a suitable mineral sample.

While Amagi publicly appears as a respected academic, he secretly operates as Dr. Machinegal, the main antagonist of the story. He appears suddenly and mysteriously in the city, using a matter-transport system called the Intrude Dimension Area transfer, which shares the same fundamental theory as the super-dimensional armor, to bring himself and his machines in and out of the city at will. He commands a personal army of destructive robots and androids, including a group of female androids known as the Machinegal Dolls, named after famous models and actresses, among them his secretary Isabella and her fellow creations. His schemes cause widespread havoc, and he has a particular passion for stealing high-tech retro devices, products of late twentieth-century electrical engineering that have become valuable antiques in his time, which he collects as a personal hobby.

In personality, Amagi is an older Japanese man with light grey hair and dark eyes, and he carries himself with a theatrical, somewhat comedic air, dressing like a classic supervillain. He is a genius whose extraordinary intellect leaves him lonely and bored, and it is precisely this isolation and boredom that pushes him into a life of crime. He delights in his larger-than-life role and treats his villainy as a kind of entertainment for himself. Despite the antagonism, he retains a warm collegial connection to his former student. He and Hiroshi share a friendly rivalry as technologists and a mutual love of old twentieth-century devices, and the two genuinely enjoy each other's company when they meet openly. The central irony of their relationship is that the heroic Moldiver users and the Machinegal group do not know each other's true identities, so the professor and his student can encounter one another as trusted old friends in one moment and as sworn enemies in the next.

His abilities lie almost entirely in his scientific genius. He developed the complex theory that shaped the city, made foundational advances in armor technology, and built the IDA transfer system that allows him to teleport himself and his forces at will. He is also a highly capable creator of androids, as shown by the Machinegal Dolls, and a strategic mind who coordinates his robot army in attacks across the city. His most notable personal weakness is his own temperament: his vanity, his boredom, and his playful disregard for consequences make him an unpredictable adversary rather than a coldly calculating one.

Throughout the series, he serves as a recurring obstacle that the heroic Moldiver users must confront, but the story portrays him less as a truly menacing mad scientist and more as an eccentric genius whose criminal career is born from a desire to escape the emptiness of his own brilliance. His development is carried by the gradual revelation of his double life, and by the layered relationship he maintains with his former student, which keeps him from simply being a villain and makes him one of the most colorful figures in the story's world.