2. A method as in claim 1 , wherein the steps of presenting collectively include operating a simulation engine having a set of state variables, and having a set of rules describing permitted changes in value of those state variables, wherein substantially each collection of possible values for the set of state variables defines a context; and the set of decision models collectively include a set of behavior models, each capable of responding to a query from the simulation engine and capable of generating a response to that query.
2. A method as in claim 1 , wherein the steps of presenting collectively include operating a simulation engine having a set of state variables, and having a set of rules describing permitted changes in value of those state variables, wherein substantially each collection of possible values for the set of state variables defines a context; and the set of decision models collectively include a set of behavior models, each capable of responding to a query from the simulation engine and capable of generating a response to that query. 17. A method as in claim 2 , including at least one of the following steps: supporting train by playing, whereby activities by a player character while playing the game are used to train non-player characters; supporting train by playing, whereby activities by a player character while playing the game are used to train non-player characters, whereby non-player characters can learn at least one of ( 1 ) actions a player character tends to take, ( 2 ) at least one context in which to apply those actions, ( 3 ) continuing learning over a time duration within the game; supporting creating teams wherein individual members of the team are trained individually by a player using train by playing; controlling or influencing actions of other non-player-entities in a game, wherein those entities include at least one of non-player characters including followers, friends or enemies; or active control elements of the virtual game; controlling or influencing the actions of a group of followers that learn at least one of (1) actions a player character takes, (2) at least one context in which to apply those actions are taken in 2D and 3D tactical/strategic action and fighting games; controlling or influencing entities that can recognize millions of different contexts and behave appropriately according to how they have observed the player behaving; controlling or influencing entities that can adapt and evolve their behavior on-the-fly and over time as behavior of the player character changes; controlling or influencing entities that can learn tactical or high-level strategic play from player characters; controlling or influencing the actions of teammates in sports games, wherein the sport might be a depiction of a known sport, or a sport with rules concocted for the video game; controlling or influencing entities that learn quickly and for whom learning can continue indefinitely; controlling or influencing entities that can learn individual skills or how to cooperate in large or small groups; controlling or influencing entities during any one of (1) a single critical decision, (2) all the time, (3) some fraction of decisions therebetween; creating behavior for entities that can be saved, restored, replayed or traded; controlling or influencing entities that can learn to make tactical decisions including at least one of: timing, spacing, approach, positioning and selection of opening moves and follow-up moves for attacks, blocks, and backing off; target selection, including double-teaming; direction and style of movement, where and when to dodge and flee; selection of a level of aggression; ordering and timing of decisions; deciding to flee or fight; controlling or influencing target selection decisions including at least one of: aiming for the heart of a cluster; aiming at stragglers; ignoring mobs to attack a leader or vice-versa; selecting which power-ups to try to obtain, selecting which crates to open or with what priority; selecting which rooms to enter or with what priority, selecting which doors to try or with what priority; controlling or influencing entities that initially at least one of (1) no knowledge, (2) very little knowledge, (3) lots of knowledge, or (4) some degree of knowledge therebetween, and thereafter learn from player characters; controlling or influencing at least one of (1) a single companion, (2) a core group of followers, (3) whole armies, or (4) anything therebetween, in response to at least one player character; controlling or influencing entities in a single player mode or in head-to-head events that show off training and leadership skills; controlling or influencing entities whose errors can be corrected by demonstration; controlling or influencing entities, wherein some user interface element, or predefined condition, specifies to which group the training signal is applied and when; controlling or influencing entities whose behavior can evolve over multiple scenarios or multiple games; controlling or influencing entities with regard to type of organization or formation, including at least one of: unit shape, when a unit chooses to engage enemies, when a unit chooses to flee enemies, whether a unit involves every soldier attacking individually or holding formation or coordinating attacks; optionally controlling or influencing entities that can learn commands from the player character; creating non-player entities that can explain their behavior; creating non-player entities that can negotiate; sharing trained characters, whereby later selection of a choice of avatars is possible for a selected encounter; allowing a player to create avatars as opponents for other players to compete with; allowing a non-player character to emulate behavior of an expert or a world-champion player character; creating and evolving a knowledge base per player, wherein that knowledge base can be loaded for a selected encounter; training a new player character by providing hints or indicators of what other player characters or scripts designed for non-player characters would do in a similar context.