This presentation examines how political leaders’ personalities change over time and how this affects governance, policies and political outcomes, particularly foreign policies. It focuses on negative developments — leaders becoming more authoritarian, more distrustful, over-confident and how this can affect aggressive and risky behaviours, and foreign policy fiascos. Temporal evolution of leaders is an important topic for international relations given the long tenure of many political leaders and their influence over politics and policies. There is very little research on how leaders’ personalities develop and how they interact with changing constraints and opportunities. The broader project addresses two primary questions: What are the main drivers behind ‘bad’ changes in leaders’ personalities and what are the effects of ‘breaking bad’? Building on research on ageing, experience, learning, and power effects, the projects tracks how leaders change, in undesirable directions, in their personality characteristics, policymaking processes, and political outcomes. The presentation will outline these ideas generally (as summarised in an International Affairs article published in 2021) and offer an application of this framework to Vladimir Putin.