The Doctor is a member of Millennium from Hellsing.The disease mind responsible for making the 1,000 armies of Vampires.
The Doctor is the Second in command of Millennium, A sick and twisted man who is mainly responsible for the experiments that have led to Millennium building their army, He is devoted to The Major and his cause.
He is also responsible for the RIP chips placed in the heads of The Majors main troops such as Jan Valentine that forces the user to combusted if he gives out information or is captured, The Doctor does not appear to have any powers, But has not aged over the years that leads us to believe that he has implanted himself with one of his own chips.
The Doctor was there when Walter and Alucard came during the world war two, to destroy Millennium, Somehow he escaped along with The Major and a few others, Hiding in Brazil the Doctor carried out his experiments creating the Letztes Battalion an army of Vampire troops.
Later on Walter C. Donez is captured , The Major turns to the Doctor and ask for Walter to be turned into one of there men, At first the Doctor disagrees saying he has not tried to turn someone with the full power of the chips yet , But does so anyway making Walter into a Freak(someone who has been given power by the chips). later after his battle with Alucard Walter is seen in The Doctors lab confronting him about the things he has created. As the Doctor tries to kill Walter he is cut down by Walters wire and reveals the truth of his research Mina Harker. It turns out that because Dracula was never killed, That Mina Harker remained infected and as she was turned by Alucard, They had been using her body to make the freak chips and vampires for their army. Realising that everything that Millennium had made was just a cheap imitation of Alucard the Blimp begins to explode a falling beam kills The Doctor as the flames engulf all of his work.