Professor Gill, also known as Gill, is the calculating and manipulative leader of a powerful criminal-terrorist organization called DARK which has an army of animal-themed killer robots called Destructoids. He plans to conquer the world by using the Destructoids originally created with the help of Dr. Komyoji.
He is a psychopathic tyrant that wanted to take over the world. Gill is without a doubt evil in nature. Like other evil leaders, Gill is arrogant, selfish and merciless in personality, to the point of having little to no sympathy towards others, including those that loyally served under him. Gill hates Paul, wanting him destroyed as a threat to his goals. Despite his hatred for the hero, he often tells Paul when playing his flute, that since Paul was born from DARK, he should return to their side.
Throughout the series, his plans ending in constant failure due to Paul and the Komyoji family caused him to become even crazier, to the point of making his subordinates take out Dr. Komyoji's brain and implanting it inside Hakaida's head.
By this point his insanity was to the point where his eyes were shown to be that of a fully crazed madman. In fact, his insanity reaches a breaking point, with it later causing him to commit suicide after DARK was defeated, in a last ditch effort to kill Paul and the others.
Professor Gill is an extremely cruel, sadistic and sociopathic bully. He is something of a misanthrope, and took to callously bullying both his henchmen and his Destructoids alike. He would go so far as to target the supremely android individuals -- namely Paul Walker -- and to lead vicious gang of androids.
Professor Gill is also extremely arrogant, narcissistic and self-righteous: a spoiled ruler, Gill would never see the wrong in anything he did, shown when he controlled Paul's Conscience Circuit, but in Gill's own eyes had done nothing wrong and violently insisted so. Even when his fellow henchmen are slightly remorseful of their cruel ruler towards Paul, Gill appears to distance from them (even to the point of shaming them as seen in the recent remake) and will do anything to make Paul's life a living hell as the lone wolf member of the group.
Gill suffered a villainous breakdown and vowed revenge, believing unshakably that his Destructoids would support him, narcissistically disregarding the fact that Paul was as strong as the Destructoids, and Gill's lack of a certain morality or restraint disturbed and repelled himself. He was very homicidal and a sadomasochist at heart, personally trying to blow up DARK with Paul inside -- as part of an elaborately sadistic campaign against the latter in the DARK base.
In pretty much all versions of the story, Gill is a tall, middle-aged man with long black or grey hair wearing a black gown. He has always with him a large bat-shaped cane which also functions as a high-pitched flute which he uses to control his robots.
Professor Gill is a megalomaniacal, black-hearted, evil, cold, insane and manipulative tyrant. Manipulating and using others, both robots and humans, to fullfil his ambitions, including his former assistant Dr. Komyoji or his own children Mitsuko and Masaru. He is very arrogant, believing no one can stand up to him and takes advantage of people and robot's weaknesses to ensure nothing goes wrong for him. Despite his hatred for Paul/Kikaida, he often tells Paul when playing his flute, that since Paul was born from DARK, he should return to their side.
While most Destructoids know that what they do is lawfully wrong (and either do not care or take pride from this), Professor Gill actually believes he is a good person. He repeatedly refuses to find fault within himself and is quite self-righteous, declaring himself much purer than everything and above everyone. He believes that everything he does is lawfully good, even as he attempts to use his evil flute to manipulate Paul.