"Yes, you were scheduled for your appointment. You checked in earlier today, and now the operation is about to begin. I'm your Doctor, refer to me as such, please. Though, my question to you is... Is there a doctor in the house?"
The Doctor, as his name is simply put, is a medical man that lives within the Hell world known as Anu-Oie, which was created by Seya. He is known as Anu-Oie's keeper, much like The Void, it must have someone to monitor the sentient dimension, though on a smaller scale, does not require to stop said deimension from destroying certain places.
The Doctor appears to be a man in his early sixties, maybe late fifties, with grey hair, and the typical pair of glasses, the white overcoat of which doctors would normally wear. He does not appear to be menacing, and uses that to his advantage, with his seemingly dry jokes and simplistic fashion, one would assume him to be a kind, elderly man.
The dear Doctor knows all about the body, depending upon species, though has not come across every single creature that has come into existence yet. He seemingly enjoys degutting others, as he actually sings, hums, or whistles a fine tune as he takes his time disembowling his victims. He also has a very dry sense of humor, as to when he first spoke to Karma, he asked her if there was a doctor in the house, to which seemingly he was the only physical doctor there.
As keeper of Anu-Oie, he makes sure to at least keep the mechanical monstrosity clean, and furnishes the place with bodies of his patients. These all give rise and strength to the sentient dimension, allowing the Doctor himself to stay immortal within Anu-Oie.
On a side note, the Doctor also tends to get excited over new patients, as when Karma checked in for her appointment, he was in awe at his first 'chance' with a Balance-Keeper. It is also noted, he finds working upon the body of others to be pleasurable, and adds that to his sadistic personality.
As simply a doctor, the Doctor himself has no special abilities, though tends to act as if he does, snapping his fingers, or making gestures, those of which Anu-Oie actually activates, what he uses is simply his brain to wrack upon the dark thoughs, feelings, and tortures upon those who he finds worth studying.