Scholars for a long time theorized about the role of political leaders, but empirical research has been limited by the lack of systematic data about individual leaders. Archigos is a new dataset with information on leaders in 188 countries from 1875 to 2004. We provide an overview of the main features of this data. Archigos specifically identifies the effective leaders of each independent state; it codes when and how leaders came into power, their age, and their gender, as well as their personal fate one year after they lost office. We illustrate the utility of the Archigos dataset by demonstrating how leader attributes predict other features of interest in International Relations and Comparative Politics. Crisis interactions differ depending on whether leaders face each other for the first time or have had prior interactions. Irregular leader changes can help identify political change in autocracies not apparent from data that consider only the democratic nature of institutions. Finally, transitions to democracy in the third wave are more likely to fail in instances where autocratic rulers were punished after leaving office. Our examples illustrate new empirical findings that simply could not be explored in existing data sources. Although selective, our overview demonstrates how Archigos bears considerable promise in providing answers to new and old research questions and opens up new avenues for research on individual leaders as decisionmakers.