Sophia is Doctor Ludvig Maxis' assistant. Sophia was revealed in one of the radio messages hidden in an underground tunnel in Der Riese. Sophia was asked to give a letter to the Reichstag High Command in the message that she was revealed in.
In Call of Duty: Black Ops, Sophia was detailed more in one of the documents seen in Dr. Vannevar Bush's account. It is revealed that she is attracted to Dr. Maxis and that he has started to view her as a distraction because he is attracted to her too.
In a hidden radio message in Kino der Toten, Doctor Maxis stated, "I catch Sophia staring at me and then she quickly glances away. I think she is a distraction from my work, and I am starting to think over having her as my assistant". This radio can be found after a select few have been activated.