Feldwebel Kurtz was a German officer at Colditz Castle. He was in direct contact with the majority of the prisoners there. He was vicious and delighted in harming the prisoners, especially ones who had tried to escape. He took particular interest in Ace when she arrived with the Seventh Doctor in October 1944, and confiscated her CD Walkman. Several times he implied that Ace should sleep with him in order to win his favour, and at one point threatened to rape her if they were alone together.
After travelling back in time from 1965, Dr Elizabeth Klein used him as a lapdog, when she sought the Doctor and Ace's cooperation. On several occasions, she threatened to have Kurtz shoot Ace if the Doctor did not comply with her demands. When the Doctor finally opened his TARDIS to her, the Doctor dematerialised it with the doors open. Kurtz was trapped between the outside world and the interior dimensions of the TARDIS, ripping him apart. (AUDIO: Colditz)