This article presents the results of studies – conducted in various countries around the world, including Poland – on the cognitive, personality, and social characteristics of a president that differentiate the effects of a presidency and how their office is exercised. The types of changes that presidents undergo while in the process of exercising their authority (i.e. the so-called metamorphic effects of power) and the mechanisms of those changes are also shown, along with the factors that determine the magnitude and speed at which those mechanisms operate. The author provides evidence for the complexity of how presidential style and execution are conditioned, and warns against committing the so-called fundamental attribution error, i.e. overestimating the role of personality in regulating the behavior of politicians. Interdisciplinary studies indicate that a president’s effectiveness is significantly ameliorated first and foremost by their openness. The weight of a president’s psychological characteristics increases in difficult situations, while the strength and extent of power’s metamorphic effects are dependent on the certainty and stability of their position in the power structure and its transparency.