Abstract: A synthetic creature (10) in which links (26), representing limbs, are loosely connected by joints (28) to independently interact and implement the physics of everyday life-like actions (18) in a character (16). Elements of mass, positive weight (46), and negative weight (48) are independently handled to mimic the closed-loop control characteristics of real animals. The synthetic creature (10) uses intelligent appearing behaviors (20) built up out of the actions (18) and recursively arranged in a hierarchical behavior tree (72) to cooperate and compete in a run-time computer (202) to give a feeling of autonomy and awareness. Further taught is an authoring environment (200) of tools used to author the character (16), actions (18), and behaviors (20) of the synthetic creature (10), which provide author feedback and simulation testing capability at the various layers (12) of the synthetic creature (10).