Abstract Designed to improve human-machine interactions, virtual agents, and particularly virtual assistants (VAs), are spreading in our daily lives. Presenting a very wide variety of characteristics, studies generally report their own agent with its own characteristics and objective. So we can wonder if some of these characteristics are a consensus for VAs in general. Within this work, we aim to identify the agents' characteristics that should be considered when designing a virtual assistant promoting the best communication and cooperation between man and machine. We review the aspects of representation of the agent (embodied or not) and its ability to interact with the human being whether by speech or gestures, but also by displaying personality traits. This overview makes some focuses on virtual assistance of any kind embarked on vehicles.