Slate has an interesting summary/review of Milton Rokeach’s book, The Three Christs of Ypsilanti (which is out of print, but shows up semi-frequently at my local Half-Price Books. Amazon wants $90 for this?)
Rokeach’s book is one of the more fascinating works of psychology I’ve read. I’d put it up there with When Prophecy Fails: A Social and Psychological Study of A Modern Group that Predicted the Destruction of the World, although the latter book is arguably more sociology than psychology.
Basically, Rokeach found three men in an asylum, each of whom believed he was Jesus Christ…and then put them together to see what happened.