Captain Von Schoenvorts
Anyone else really, really like this guy? At the time the movie was made he was a welcome change from the "Rrrrraaahhh, Germans BAD!" cliche in movies set during either World War, and he's also a step up from Burroughs' novel. Don't get me wrong, I love the book, but Von Schoenvorts is such an insufferable dick in it. When they made the movie, all of Von Schoenvorts' bad traits got transferred to the movie-only character of Dietz, so the story was still able to have a German officer who was a big fat jerk, but also have one who was relatively resonable and insightful.
I think my favorite scene with him is when he's explaining to Lisa why he torpedoed the British ship:
Lisa: That ship you torpedoed contained nothing but innocent passengers! Women and children!
Von Schoenvorts: And a hold full of arms and ammunition that would've have been used to kill women and children in MY country.
Not saying he's a saint or anything, just that the screenwriter (not to mention the actor) did a commendable job on making Von Schoenvorts feel like an actual person, with both good traits and bad ones, as opposed to the cardboard cutout villain he was in Burroughs' book (Dietz fills THAT role in the movie, as noted).