Dr Tanizaki was a Japanese doctor studying cybernetics. In 2007, Ianto Jones hired him to help reverse Ianto's girlfriend Lisa Hallett from her conversion into a Cyberman. He had shown 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. (TV: Cyberwoman)
