Laurence Olivier plays Dr. Christian Szell, a Nazi dentist, who is clearly based on the real life Nazi Dr. Josef Mengele. Olivier is probably the best part of Marathon Man, and his performance creates a very memorable villain in Dr. Szell. Olivier gives an incredibly interesting performance, one reason is because he never goes over the top. Playing a Nazi Dentist it would have been incredibly easy to go over the top but Olivier never does despite the strange role he has. His accent uses is very effective as an incredibly quiet German accent that he does. He never sounds stereotypical, and the accent works perfectly.
Olivier is only ever subtle, and understated as Szell making his performance far more effective and disturbing than if he went over the top. He almost always stays quiet in the role, making everything he does always a little more intense, since it is not obvious what he is going to do. He plays Szell certainly as an evil man, but still a man. He does not play as some monster, but as an old man who happens to pure evil. Olivier is always effective because of this. Every scene he is in becomes interesting because of him. The scene where he tortures Babe (Dustin Hoffman) would not be nearly as chilling if it were not because of Olivier's perfect way of speaking in these scenes. Is it safe would not be as memorable as it is if it were not for the way Olivier speaks it. His delivery is so perfectly chilling, since he always understates it. He never yells is it safe, but just coldly states it creating far more effective scene.
Olivier is in full control throughout the performance. Every movement and gesture he makes is always finely attuned and helps his performance. Even though it obviously is acting he never seems to be doing so. All his movements all work for the character and merely add to performance even more so. Olivier shows the joy of his performance in this performance. Even though he is playing a despicable character, Olivier always shows the proper amount of life in the character. He shows that Szell know who he is and enjoys it. Szell is not a purely one note villain and I believe a strong reason for that because of Olivier's brilliant performance. Olivier never falters from when Szell knows all and is in command to when he loses his power just right at the end creating a satisfying conclusion to the character. Another great performance from the great Olivier.