IST has been building computer generated humans—combatants and civilians—to populate a virtual battlefield as part of the Team Target Engagement Simulator (TTES) project. This project, which is sponsored by the Naval Air Warfare Center Training Systems Division in Orlando, will train small infantry units to fight in urban terrain. Such a low level simulation with direct human involvement requires detailed models not only of terrain and human behavior but also of human physical characteristics. This paper presents an overview of the problems that a designer of computer controlled humans must address to create realistic entities. The problems span all levels from low level modeling to cognitive behavior. At the simulator infrastructure level we discuss DIS representation and urban terrain databases. At the physical environment level models of visible line of sight, sound generation and propagation, weapons effects, and movement are important. The next level addresses physical entity characteristics and requires modes of vision, hearing, movement, wounds, and fatigue. The last level is cognitive, and comprises two parts: automatic behavior such as perceptual processing, feedback-based motion control, and weapon aiming; and deliberate problem solving and action selection. The paper briefly describes our approach to building all of these models.