Professor Gill is the principal antagonist of the anime Tobidasu Jinzō Ningen Kikaidā, a sinister and brilliant roboticist who commands the evil organization DARK in its quest for world domination. His background is that of a leading scientist whose genius became twisted toward criminal ambition. He once funded the robotics research of Dr. Kōmyōji, intending to trick the respected scientist into building a force of robot slaves for DARK. When Dr. Kōmyōji would not cooperate, Gill had him taken prisoner and forced him to design destructive android weapons for the organization. During that captivity, Dr. Kōmyōji secretly built the android Jiro, who would become Kikaider to protect his creator's children and oppose Gill's plans.

In personality, Gill is calculating, manipulative, and cold-blooded. He is deeply arrogant, convinced of his own intellectual superiority, and regards both people and machines as disposable instruments in his scheme to conquer the world. He treats independent will and emotion as flaws, which is why Jiro's choice to rebel and fight for justice enrages him. Gill sees Kikaider not merely as an obstacle but as a personal insult, a creation that rejected its intended purpose, and he becomes determined to destroy the android he regards as his own property.

Gill's role in the story is to orchestrate the continuing attacks against Kikaider and the children of Dr. Kōmyōji. He directs DARK from its base and deploys a steady stream of animal-themed androids called Destructroids to hunt down the hero and silence anyone who opposes him. His most notable ability is his mastery of robotics and engineering, which allows him to design, build, repair, and mass-produce new robot killers and adapt his weapons to counter Kikaider's fighting style. He is also known for using a special flute that can control the androids of DARK and inflict intense pain on Jiro, disrupting his ability to transform into Kikaider, forcing the hero to find ways to resist or drown out the sound. Gill himself rarely enters direct combat, relying instead on his intellect, his remote command of the organization, and his mechanical creations.

Gill's key relationships define the conflict of the series. With Dr. Kōmyōji, he acts as an exploiter and captor, forcing the doctor's talents to serve DARK while holding him prisoner and threatening the people close to him. With Jiro and Kikaider, he is simultaneously creator and nemesis, a sinister father figure who views the android as his possession and reacts with fury to Jiro's independence. Through their repeated confrontations, Gill proves himself relentless, refusing to accept defeat even as Kikaider continues to foil his schemes and defend the innocent.