Abstract: Adaptation (online learning) by autonomous virtual characters, due to interaction with a human user in a virtual environment, is a difficult and important problem in computer animation. In this article we present a novel multi-level technique for fast character adaptation. We specifically target environments where there is a cooperative or competitive relationship between the character and the human that interacts with that character.In our technique, a distinct learning method is applied to each layer of the character's behavioral or cognitive model. This allows us to efficiently leverage the character's observations and experiences in each layer. This also provides a convenient temporal distinction between what observations and experiences provide pertinent lessons for each layer. Thus the character can quickly and robustly learn how to better interact with any given unique human user, relying only on observations and natural performance feedback from the environment (no explicit feedback from the human). Our technique is designed to be general, and can be easily integrated into most existing behavioral animation systems. It is also fast and memory efficient.