We describe a framework for creating animated simulations of virtual human agents. The framework allows us to capture flexible patterns of activity, reactivity to a changing environment, and certain aspects of an agent personality model. Each leads to variation in how an animated simulation will be realized. As different parts of an activity make different demands oil an agent's resources and decision-making, our framework allows special-purpose reasoners and planners to be associated with only those phases of an activity where they are needed. Personality is reflected in locomotion choices which are guided by an agent model that interacts with the other components of the framework.