Laurie Hutzler once gave a workshop on the emotional toolbox, a way of developing characters on screen, and I think its an interesting approach. Here is a link to her website, which has some free blog posts which show you the basics of her ideas. Characters begin as their masks, have a want which drives them to act in act two and gradually their true character emerges.
Brad Pitt in Thelma and Louise has a mask of a polite student who wants a lift back to college but we learn he is a charmer and a con man who sleeps with Thelma and then robs her. Can you think of other examples. /