This article describes the use of objective psychological instruments, including the Revised NEO Personality Inventory (NEO PI-R), to assess the personalities of all 41 U.S. presidents to date. We briefly report our findings pertaining to the average profile of chief executives on the NEO PI-R and summarize data on two of our most illustrious presidents, Washington and Lincoln. We review a typology of presidents based on our data. Finally, we summarize the results of our investigation of the Big Five personality dimensions and facets that are related to presidential success (i.e., historical greatness). The project and findings are discussed in terms of the use of the NEO PI-R in psychohistorical research and assessment.