While most discussions of incivility in the workplace focus exclusively on deviant behavior and its negative consequences, this paper introduces the behavior of a particular type of employee who has a powerful negative impact on morale, yet remains highly productive on measures of task performance. This employee type is labeled "Dementor" (adapted from a recurring type of character found in J. K. Rowling's series of Harry Potter books). Dementors are high-knowledge, high-skill employees driven to overachieve by low self-esteem and other personality influences that can be exacerbated by situational characteristics. The highly productive Dementor deliberately attempts to lower the productivity of coworkers to alleviate the Dementor's own performance anxiety. This paper offers an overview of Dementor behavior, discusses individual and organizational influences on Dementor behavior, describes the impact of the Dementor on the organization and on individuals within the organization, and offers practical strategies for managing the Dementor in the workplace.