Major Horst Mohn was a Luftwaffe; paratrooper officer and a hero from the Eastern Front, as well as fighting in Belgium, Crete, and Greece. He had been badly wounded fighting in Stalingrad,which a Russian soldier, had bayoneted him in the stomach, before Mohn shot the soldier in revenge. He was on the last plane that left Stalingrad, and returned to Germany a celebrated hero, and briefly become part of Hitler's personal staff.His wound caused him discomfort and made eating difficult. He also had difficulty sitting down. Despite being a Luftwaffe officer, he eventually arrived at Colditz to serve as the Kommandant's second in command.
An extremely arrogant man who idolized Adolf Hitler, Mohn respected but openly disagreed with the Kommandant. His relationship with his colleague and subordinate Hauptmann Franz Ulmann could best be described as tedious, while Mohn's treatment of the prisoners was often cruel and callous. Despite his loyalty of the party he fears the Gestapo and was shocked on the execution of the Allied prisoners, as well as the execution of the Jews, which he sees as excessive, but will come to pass.
He also constantly finds himself in conflict with the Kommandant, for he holds the philosophy that the war is still going on at Colditz and is frustrated by what he perceives as the treating of prisoners with "kid gloves". The prisoners loathe him, and do whatever they can to foil him or antagonise him at every turn. Unfortunately for them, he is as intelligent, as he is ruthless and occasionally pulls off a devastating capture. Major Mohn is a paratroop officer and his relationship with the SS appears to be fairly chilly. He is visibly upset with the SD orders given at the end of the episode "The Guests" and seems nervous around Obergruppenführer Gottlob Berger and Hauptsturmführer. It appears that the reason why Major Mohn would prefer to take SS orders unquestioningly than risk SS reprisals is that he appreciates, apparently better than the Kommandant, what the SS is capable of.
When he first arrived he also indicates that Hitler was informed of the successful escape attempt and insists that security be tightened up, thus sending a member of his own personal staff to ensure this. Mohn also had a hand in manipulative events as he used the kommandant to have the British commandos sent to Colditz, due to him correctly predicting that the British contingent would attempt to help the commandos escape, and use their best escape plan, the one used by Pat Grant and Phil Carrington to make their home run.
When Germany began losing the war and it seemed as if Colditz was soon to be taken by American forces, and Mohn's belief in the Nazi cause was visibly shaken when he learns that his brother died ignominiously, crushed by a Russian tank. He also learned from Ana, an old friend, and her brother who tell him the war is lost, and that her brother had just come from Dresden, and showed him the image of the victums of the bombing, causing the brother to tell him; 'it's every German for himself!' Mohn tried in vain to get in good favor of the prisoners, but the list of crimes that the prisoners put together along with their hatred of him, and the fact he was a member of the party would lead to his conviction. Mohn fled in disgrace after being relieved of command it is unknown what happened to him later it could be assumed that he escaped to Argentina with the money he had in Switzerland.
- Knight's Cross of the Iron Cross with Oakleaves and Swords
- Iron Cross 1st Class
- Wound Badge (Gold)
- German Cross (Silver)
- Luftwaffe Paratrooper Badge
- Close Combat Clasp (Gold)
- Wehrmacht Long Service Award
- Sudetenland Medal
- Anschluss Medal
- Kreta Cuff Title
- The dark green service colour of his collar tabs and on his shoulder boards show his branch of service as a member of a Luftwaffe Field Division.