Dr. Paul Ekman

Paul Ekman is a famous doctor who has performed extensive research on facial expressions and emotion. He has written over 100 articles on emotions and facial expressions. He is the man who claims there are 7 universal facial expressions. Because of his extensive background in facial expression and emotional research some may consider him an expert. 

                                                         
This picture was borrowed from http://www.paulekman.com/wp-content/uploads/2009/02/pekman.jpg