I start with actors that I know personally or I know their work, and there are things about their work or their presence or their own personality that make a character, that exaggerates some qualities and suppresses other qualities. It's always a real collaboration for me.
I do believe that in order to be a successful negotiator that as a diplomat, you have to be able to put yourself into the other person's shoes. Unless you can understand what is motivating them, you are never going to be able to figure out how to solve a particular problem.