Persecutor alters in dissociative identity disorder are uniformly described in behavioral terms as belligerent, abusive, and violent. While most authors agree that persecutors begin as helpers there is no consensus about their later development or function within the system. This paper presents a theoretical model of the etiology and development of persecutor alters. It elucidates the underlying and continuously protective nature of the alter which becomes masked by the apparently "persecutory" behavior. Using clinical examples which build on their appreciation of the positive function of persecutor alters the authors present their treatment techniques, which include: engagement, building rapport with the underlying protective function, psychoeducation of the alter, and finally, family therapy style negotiations of roles, expectations, and boundaries. The paper concludes with an examination of the countertransference issues which commonly arise in working with persecutor alters and their impact on the clinician and the therapeutic task.