Professor Gill is the main antagonist of the 1970's manga Android Kikaider by Shotaro Ishinomori as well as its tokusatsu and anime adaptations.
He is the leader of a powerful criminal 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 Prof. Komyioji and a gigantic robot called the Giant Devil (also known as Armageddon Lord).
After being fatally wounded at the end of the first half of the saga, the last surviving DARK scientists transfer his brain inside Hakaider's body, thus becoming Gill-Hakaider.
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.
His brain is later transferred into Hakaider's body.
Gill is a megalomaniacal, cold and cruel. Manipulating and using others, both robots and humans, to fullfil his ambitions, including his former assistant Prof. Komyioji or his own children Akira and Rumi. 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 Jiro/Kikaider, he often tells Jiro when playing his flute, that since Jiro was born from DARK, he should return to their side.
In the 1970's live action series, Gill is depicted as more wrathful and unstable than his manga and anime counterparts.
In Kikaider 01, Gill returns as a new incarnation of Hakaider, leading a team of color-themed Hakaiders called the Hakaider Force. The other Hakaiders were the DARK scientists who transferred Gill's brain in the original Hakaider's body. They plane to kidnap Gill's son Akira because he has the plans for the Giant Devil robot tattooed on his back (in the anime the purpose of Akira was being the living battery for the Giant Devil).
But the Hakaider Force's plans are thwarted by Kikaider/Jiro and his older brother Ichiro/Kikaider 01.
After the destruction of the Hakaider Force, Gill is forced to become a member of a new evil organization called SHADOW.