Kurtz

Feldwebel Kurz was a German officer at Colditz Castle. He was in direct contact with the majority of the prisoners there. He was vicious, delighting in harm to the prisoners, especially ones who had tried to escape. When the Seventh Doctor and Ace arrived in the Castle by accident in October 1944, he took a particular interest in her and her contraptions, dismantling her a CD Walkman. Several times he implied that Ace should sleep with him in order to win his favour, and at one point implied he would rape her when they were alone together (but she escaped before they were ever 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, Klein threatening 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 between the outside world and the interior dimensions of the TARDIS, ripping him apart. His death appalled Ace. She began referring to herself by her birth name, Dorothy McShane. (AUDIO: Colditz) She later described his death as one of the worst things that she had ever seen. (AUDIO: The Rapture)

In Klein's timeline, Kurtz was successful in his attempts to kill Ace. (AUDIO: Colditz, AUDIO: Klein's Story)