Abstract: Certainly non-player characters (NPCs) can add richness to a game environment. A world without people (or at least humanoids) seems barren and artificial. People are often a major part of the setting of a game. Furthermore, watching NPCs perform and have a life outside of their interactions with the main character makes them appear more reasonable and believable. NPCs can also be used to move forward the storyline of a game or provide emotional elements. Authoring NPCs can, however, be very laborious. At present, games either have a limited number of character profiles or are meticulously hand scripted. We describe an architecture, called CAROSA (Crowds with Aleatoric, Reactive, Opportunistic, and Scheduled Actions), that facilitates the creation of heterogeneous populations by using Microsoft Outlook$textsuperscript textregistered $, a Parameterized Action Representation (PAR), and crowd simulator. The CAROSA framework enables the specification and control of actions for more realistic background characters, links human characteristics and high level behaviors to animated graphical depictions, and relieves some of the burden in creating and animating heterogeneous 3D animated human populations.