Among the most important factors governing enjoyment of computer games is immersion, or the feeling the player has of being in the game world. This feeling allows the player to be transported into the world of the game, where they can experience grand adventures and riveting tales. Many factors contribute to the feeling of immersion, but as with any story-based experience the actors in the story are of the utmost importance. If the actors perform poorly, however, the player's feeling of immersion will be lessened, and the game will become less entertaining. Therefore, the Non-Player Characters (NPCs) inhabiting the game world must act in such a way that they are perceived as believable. Unfortunately, this is not always the case, and NPCs often disrupts the player's feeling of immersion.
The purpose of this research is to describe how we can create NPCs who behave in ways that are conducive to player immersion, and who better portray the story of the game. This is done by identifying the current issues affecting the believability of NPC behavior.
Over the course of the studies described in this thesis, we have developed a method by which problematic behaviors can be identified and described. This was done by studying NPCs in modern games using video recordings, and using an analytical tool to identify the specific factors that affect the believability of their behavior. In the end, we identified a number of such factors that affect the believability of NPCs, chief among them the inability of NPCs to perceive the world. By improving the way in which NPCs perceive the world, and more importantly how players perceive that NPCs perceive the world, we can greatly improve NPC believability.