In this study we aim to describe in what ways non-player characters (NPCs) affect believability. To this end, we have conducted an online survey, where respondents were asked to classify and describe NPCs. Furthermore, we also examined recordings of NPCs in games. These data sources were examined using a model for NPC believability in order to describe the effect on believability by different types of NPCs. Based on this, we were able to construct a model of NPC believability, based on the NPC’s level of complexity and ability to handle a mutable social context. As described by the model, NPCs are currently less capable of handling changing social contexts. They do, however, show promise, and given current emerging technologies it is feasible that new types of more socially capable NPCs will arise within the near future.