Twenty years ago, Robert and Joyce Hogan introduced the concept of the dark side of personality as a way to understand incompetent management and bad leadership. The current article traces the development of this line of thinking and highlights 6 lessons learned from 2 decades of research inspired by it: how to define and assess the dark side of personality, the distinction between identity and reputation, the distinction between leadership emergence and leadership effectiveness, the dark side of charisma, the overlooked but pervasive problem of absentee leadership, and the crucial distinction between competition within groups versus competition between groups in the evaluation of leadership. The dark-side perspective helps correct a positivity bias in leadership research and provides insights for improving team, organizational, and national performance by minimizing the selection of the wrong people for leadership roles and enhancing the self-awareness and self-management of those in leadership roles. (PsycInfo Database Record (c) 2021 APA, all rights reserved)