Do Virtual Humans Dream of Digital Sheep?

As human beings, we are so used to interacting with each other that any world without humans would feel alien to us, including digital ones. In this article, we present a survey on the role of digital human-like characters in virtual worlds, both as counterparts of real human users and as embodied agents driven by artificial intelligence. The main issues related to 3-D graphics, physics, animation, and behavioral modeling are introduced, suggesting wherever available different alternatives and related development pipelines. A sizeable list of examples illustrating the use of virtual humans in different application sectors is then presented, focusing in particular on four domains: environmental design, training, cultural heritage, and healthcare.