Doc usually appears dressed in a perpetually bloodstained white labcoat, an unusual shirt which reveals his stomach, and glasses with an assortment of adjustable, multilensed spectacles. He is Millenium's top scientist of physiology and technology, the genius behind many of their projects. Perhaps unstable, certainly eccentric, but undeniably brilliant. It was his research that led to the creation of a Nazi vampire army out of 1,000 volunteers in the 'Letztes Battalion'. Hirano has stated that he created Schrödinger, which goes well with his 'mad scientist' reputation. The two argue almost constantly. He appears in the manga and OVA series, and as a silhouette to the right of the Major in the promotional video (found on the first DVD of the English release). It is possible that the Doctor created the Major's cyborg body, but it is currently unknown as to whether he is also an android or something else.
Per his nametag shown in Volume 3, his name appears to be Avondale Napyeer. The nametag is difficult to read, however, and no other name has been given thus far.
It appears that based on Chapter 93 that The Doctor is going to release "She", the enigmatic, heavily bandaged figure from Hellsing: The Dawn.
At the end in chapter 94 arguing with Walter about how useless he was, that one day he will overthrow and defeat Alucard and that he's being a failed experiment Doc tries to press a button from its remote to kill Walter but he uses its wires and cuts off docs arm and leg making him fall to the ground and take off the blanket of the SHE and revealing she was Mina Harker used to start their experiments and trying to defeat Alucard (or as Walter said "trying to imitate him") Then we see that a part of the construction falling apart and smashing Doc killing him instantly.
He may be based off of the infamous Nazi Physician Josef Mengele.