Embodied conversational agents are synthetic characters that resemble humans not only in their physical appearance, but also in their behaviour with more or less the communicative characteristics of real persons. They are gaining much interest, both as mediums to visualize models of human communication, and as interfaces in different applications. The first steps have been taken in the direction of expressive ECAs, by endowing them with the capability of showing emotions.

Subtle issues such as the impact of social role and personality have also been addressed. Non-verbal signals have been used to accompany speech to make a virtual human more expressive and believable, but, these works concentrated on modeling the psychological, social and communicative aspects of emotional and cognitive state. Usually the presentational issues are not dealt with as a research topic, but as a practical task for an animator, often only to make a specific application or demonstrator. Moreover, most of the agents created so far are generic: it is difficult to differentiate them by the way they move, answer, react? It can be said that most of the time, they all "come from the one mould".