Barbara Kellerman is a lecturer at Harvard University's Kennedy School of Government who studies leadership and followership. She identifies five types of followers based on their level of engagement: Isolates, who are completely detached; Bystanders, who observe but do not participate; Participants, who are engaged in some way; Activists, who feel strongly about their leader and act accordingly; and Diehards, who are prepared to die for their cause or leader. Kellerman analyzes followers based on their rank or behavior relative to their leader. Her typology aims to understand different levels of follower engagement and the implications for leaders.