Dr. Sebastian is a ghoul with such grotesque appearance, even other ghouls flinch at. However, his grotesque features perfectly match his twisted obsession with finding a repeatable and successful way to procreate ghouls. He savagely goes through human hosts like a butcher in a slaughter house, but with far more verve. He thoroughly enjoys poking, prodding, cutting, and generally making his victims feel as uncomfortable as possible.
Before he became a ghoul, Sebastian was a prominent, upscale plastic surgeon. When Willem Clark found him during his long trek, Dr. Sebastian was trying to graft a dead human’s smooth skin on to his own as a means to at least look human. Willem eventually convinced Sebastian to embrace his ghoul-ness, and to look upon it as a step further into evolution. Sebastian bought into the teaching of the charismatic Willem Clark and followed him back to the Reservation. Many years later, after the ghouls discovered they could not procreate, Willem and Sebastian decided to find a way to remedy that. Through extensive research and experimentation, they concluded that the smoothskins would have to serve as catalysts of some sort for any ghoul procreation process. From then on, Dr. Sebastian made it his life’s mission to find a successful and repeatable way to procreate ghouls. Sebastian will stop at nothing to find a solution to the ghoul procreation dilemma, and he will go through every human until none remain, if that is what it takes. Of course, if there are no humans, then his experiments will cease - but his obsession overshadows this logic.
In addition, Dr. Sebastian is most proud of his last successful born ghoul, Belle. She is disturbingly attractive to human eyes, and a complete knockout to the ghouls. In fact, Belle could almost pass for human on a dark night, or in a low light room. This attractiveness, coupled with her ghoul-like traits of radiation immunity and gifted abilities, is exactly the direction Dr. Sebastian wants to take the procreation experiments. There’s even hope in his rancid heart that Belle can conceive, though "relations" with other ghoul volunteers has proven fruitless. However, the non-ghoul Prisoner, through certain conditions, can make this dream a reality.
Dr. Sebastian has not appeared nor is he mentioned in any published game. He was to appear only in Van Buren, the canceled Fallout 3 by Black Isle Studios. It is not certain if he will appear in any future Fallout game.