My nonprofit management professor has a theory that the personality type most likely to be involved in trying to save the world is an ENFJ. He demonstrated this by showing the results of a Myers-Briggs test he asks all of his nonprofit students to take every year. Apparently, about 24-25% of the people in his nonprofit classes are consistently ENFJs, even though this personality type makes up only about 2-3% of the country.
I found this fascinating, and may try to see if there is any other research or information about this phenomena out there. I would also love to compare the personality types of people in different volunteer or leadership positions to see what patterns emerge between interests and skills and roles.