We describe the architecture of an interactive, “believable” agent with personality, called user agent, which can act on behalf of a user in various multi-user game contexts, when she is not online. In a first step, information about the personality of the user is obtained from a questionnaire and then, in a second step, integrated in the reactive system of the user agent, part of which implements a primitive affective system. User agents can interact with their users through a simple affective natural language generation system (SARGS), which is integrated in the deliberative system of the user agent and can recount what happened to the user agent in the game while the user was not present.