Psychoanalysis, a favorite method for studying personality and motivation, cannot be used on the dead. Instead, biographical analysis must be employed. This study examines Mark Twain's aggression by analyzing his writings, social behavior, and environmental aspects of his life. In viewing Mark Twain's novels as representing fantasy, 17 categories of aggression are discernible. Mark Twain's letters to his wife, friends, and publishers may represent reality. Content analysis provides a quantitative measure of motivation of aggression. Three categories of motivation examined are self-aggression, moral outrage, and teasing. A comparison of Twain's fantasy and reality suggests that: (1) there is a dimension of overt versus non-overt aggression that provides a response hierarchy in which object-directed playful non-overt aggression is subordinate to serious overt aggression; (2) when the self is perceived as the frustrator, but there is constraint on the social expression of aggression, the aggression will be displaced in the form of self-aggressive fantasy; (3) when other persons or social institutions which have personal representatives are perceived as the frustrating agents, and there is serious constraint on social expression, the displacement will take the form, in fantasy, of moral outrage directed toward people in authority; and (4) when the frustrating circumstances are both implacable and relatively impersonal, constraint on expression of aggression will force its displacement into moral outrage and self-aggression in both fantasy and reality. (ABL)