Kramer was a Waffen-SS colonel who was the Deputy Chief of the German Secret Service and the ranking officer at the Schloss Adler. Soft-spoken and practical-minded, Kramer was initially in charge of interrogating the captured General George Carnaby, but, in the interests of fostering cooperation between the SS and the Heer, and also intent on keeping Captain von Brauchitsch out of the loop, he sent word to Berlin, leading to the arrival of Kramer's old friend Reichsmarschall Julius Rosemeyer. This and other things kept from him angered von Brauchitsch, but Kramer paid him no heed.
They convened in the Golden Hall of the Schloss Adler. Uncharacteristic for an SS officer, Kramer wished to avoid torture. When Carnaby refused to tell them about the Allied plans for the second front, Kramer had Olaf Christiansen, Lee Thomas and Edward Carraciola brought in, hoping that having three of his supposed rescuers revealed as Nazi spies would break the General's spirit. Still Carnaby refused. Annoyed, Kramer told Anne-Marie, his secretary as well as a nurse, to begin torturing the General. No sooner had they begun than two strangers appeared. One introduced himself as Johann Schmidt, an undercover SS agent, who revealed that his partner was American assassin Morris Schaffer, who he forced to drop his gun.
Next, Schmidt told Kramer and the others that "General Carnaby" was actually Cartwright-Jones, an American actor impersonating the real Carnaby to give the Nazis false information, and that Christiansen, Thomas and Carraciola were also imposters, which the three fervently denied. Schmidt proposed that if they genuinely loyal Nazi spies then they'd know the names of their contacts in Britain. While they compiled the lists Schmidt asked for, Kramer summoned a guard he could trust, Sergeant Hartmann.
But as soon as "Schmidt" got the lists, he knocked out Hartmann and revealed he was really British spy John Smith. Although "Carnaby" was still a fake, Christiansen, Thomas and Carraciola were genuine, and the lists of names were the true purpose of the mission. Kramer was stupefied and incensed. Captain von Brauchitsch came in, but was overcome thanks to the timely arrival of Mary Ellison. Captured, Kramer was given a choice: be shot or be injected with Nembutal, which would knock him out for a while. He chose the latter. Along with Rosemeyer, Anne-Marie, Hartmann and von Brauchitsch he was administered the drug and fell asleep.
They were found later by a corporal sent to alert Kramer to the fact Allied agents had broken into the castle - something the soundly sleeping Kramer was already aware of. His fate after this is unknown.
In the film, Kramer doesn't survive. When Schaffer shoots Major von Hapen, Kramer tries to call for help on his personal telephone, and is shot twice by Schaffer to stop him, killing him.