We review in detail the generally unknown, and unrecognized, historical involvement of Fairbairn's thinking on multiple personality disorder with the development of his mature object relations theory of endopsychic structure during the period from 1929 to 1954. We describe the development of Graham Clarke's attempt to make Fairbairn's model consistent with Freud's topographic categories. We propose an extension of Fairbairn's original theory to address some common clinical features of multiple personality. The extension explains the origins of alter personalities from within the theoretical framework of Fairbairn's psychology of dynamic structure. This extension of Fairbairn's original theory proposes trauma-induced, structure-generating processes that produce dissociated alternative personalities. We believe that this proposal is helpful in the understanding of the origins of alternate personalities, provides a framework for their mapping, and facilitates the appreciation of the relationships that are typically found to exist between them.