“The only part that was really hard to cast was Himmler,” Randau tells THR. “I was looking for someone who could play a weasel kind of guy, but it was really, really tough.” So, the film doesn’t show the real horror of Heinrich Himmler because it’s told via Felix Kersten. People talk about Heinrich Himmler as someone who saw himself as a mathematician of the Holocaust. And keep in mind: It’s not the ‘true’ Heinrich Himmler in the film.