Tanizaki

Dr. Tanizaki was a Japanese doctor studying cybernetics who Ianto Jones hired to help reverse his girlfriend Lisa Hallett from her conversion into a Cyberman. He showed a keen interest in the Cybermen ever since the Battle of Canary Wharf.

He died when Lisa tried to "thank" him by removing his human weaknesses by converting him into a Cyberman, which was horribly botched. (TW: Cyberwoman)