Non-Player Characters

Diegetic persons in game worlds that are not controlled by players.

Note: the use of characters in this pattern and the pattern named Characters differs. Here, the usage of character complies to the common usage in the gaming community of referring to the graphical representation of a person in the game world (a sort of non-player version of the Avatar patterns). Although the common usage may also often imply the presence of the Agents and Characters patterns, this is not necessary and not presumed when used here.

Note: the abbreviation NPCs is very common for Non-Player Characters and is used here as well.

Examples

The later instances in the Elder Scrolls and Fallout series have NPCs that have daily routines, go through the actions of eating and sleeping, and have short conversations with other NPCs. They also have allegiances to various social groups and will come to the defend of other members of these groups if they are attacked.

Torchlight

Black & White series

Fable II

Façade

Need for Speed Series

Super Mario series

The Legend of Zelda series

Thief series

World of Warcraft

Sometimes the issues of whether a diegetic person is an NPC or not depends on the play mode, and can be mostly a subjective opinion. For example, when playing the Left 4 Dead series with other players it is quite clear that they are not NPCs but when playing one of these games alone offline they are more likely to be treated as NPCs. Playing alone online is more unclear since other players may join but one does not know that until after the fact (one could argue that the designers see them as NPCs in this case since the server shuts down if one disconnects). Although example of a borderline case is in the Sims series; any Sim in the active household can be controlled by a player but does not need to be, and Sims from other households created by the same player may come for a visit but do this as pure NPCs.

Using the pattern

Non-Player Characters most important characteristics are which role they play in relation to the players and the Game World they inhabit. Since some NPCs mainly have roles as extras or specialized Self-Service Kiosks, this somewhat paradoxically mean that it is not necessary for all Non-Player Characters to be Characters. Instead, it may be more important that they can recognized during gameplay for what they are, which for NPCs that are supposed to individually distinguishable probably means that they need to have Diegetically Outstanding Features. The lack of Character does not mean that they cannot play essential parts of Narration Structures, they can perform these roles through Cut Scenes. In fact, through the use of Cut Scenes NPCs can be part of games even if they rarely or never can be perceived or interacted with in the actual Game World. One specific example of this is Browser in many of the Super Mario series, he is typically encountered early during gameplay and then several times through out the game through Cut Scenes but is only possible to interact with him as a Boss Monster during the final fight of the game.

A primary choice when designing NPCs is whether they should have agency within the Game World. Making them Agents is typically achieved through the use of Algorithmic Agents or Game Masters, but can sometimes be done through Spectators (especially in games with Pervasive Gameplay, e.g. Prosopopeia). An additional option to adjust the level of agency is to consider giving the NPCs Initiative, although this may lead to a lose of Predictable Consequences. When NPCs have agency, they can take the opposing roles of Enemies (and Boss Monsters) or supporting ones of Companions by giving them Preventing and Supporting Goals respectively. The role of Enemies can make it possible to allow activities requiring many participants, e.g. Races or King of the Hill competitions, in Single-Player Games although in contrast to Multiplayer Games this is typically done as part of some Meta Game where the player can improve Skills or Abilities. The use of Companions can be predetermined by Narration Structures or the Reward of successfully completing Gain Allies goals. NPCs used as Companions can also affect Narration Structures by having Linked Destinies or being the cause of Internal Conflicts for players. The options players have in interacting with NPCs can through these means easily be made into Character Defining Actions.

Even without agency NPCs can provide many different types of opportunities for interaction with handling Trading and the assignment and adjudication of Quests being common. Likewise, they can be important parts of goals through being the senders and receivers in Delivery goals, being the objectives of Evade, Rescue, or Guide and Protect goals, by making up the pool of possible candidates in Match-Making goals, or the receivers of Binding Promises to make Committed Goals diegetically present in the Game World. When the NPCs only can perform these actions (due to not having agency) they are in principle Self-Service Kiosks for the players.

Providing NPCs with a Character is related to the choice of giving them agency but can be done independently. Characters without agency can provide Complex Gameplay but does so without forcing players to become reactive. ELIZA can be argued to be an example of this although this is achieved through a set of response rules rather than through abstract characteristics. Adventure games such as The Secret of Monkey Island and the first instances in the Fallout series can also be said to do this, but through Dialogues in this case. NPCs which are Agents with Character typically provide even more Complex Gameplay, as for example found in the Sims series and later installments of the Elder Scrolls and Fallout series.

Being able to engage in Dialogues with NPCs is a common functionality. This may be as simple as a Canned Text Responses to show that they have nothing important to say (but makes finding NPCs with something to say a form of Exploration goal) but can also be the primary type of interaction (as in, for example, ELIZA and Façade). Besides allowing Narration Structures to unfold, typically uses of Dialogues include: giving, supporting or finishing Quests; or providing Gossip to either indicate Optional Goals or showing Memory of Important Events (e.g. Persistent Game World Changes). For games supporting more Complex Gameplay through the use of Dialogues, the specific challenges of False Accusations or Brokering and the goal of Maintaining Lies are possible.

One of the uses of NPCs is to create Factions that players can interact with or become members of. The goal to Gain Allies can also be modified so that successfully completing it results in a whole Faction becomes an ally rather than a single NPC, and actions towards individual NPCs can easily become Character Defining Actions since they can affect a player possibilities to interact with a whole Faction. Individual NPCs can has special statuses in these Factions by being Social Gatekeepers, competitors in situations of Internal Rivalry, or by secretly being Traitors. Having NPCs in Factions, or at least implicit ones through a willingness to talk to each other, make it possible to modify many of the gameplay possibilities of Dialogues to be possible through Eavesdropping (possibly requiring the completion of Stealth Goals).

More generally, NPCs can be used to make the culture and social norms of Game Worlds part of the gameplay through Diegetic Social Norms. This make it possible that Actions Have Diegetically Social Consequences, e.g. assaulting people in civilized areas provoke attacks from the law authorities as in the Assassin's Creed or Elder Scrolls series. While this can regulate which actions are not socially acceptable, and when, by the NPCs, Diegetic Social Maintenance can be used to make it socially unacceptable to not perform certain actions according to some rule set. All of these can be applied on both general levels and on Faction levels, creating more Complex Gameplay by making players need to handle competing and possible incompatible social rules.

My Enemy’s Enemy is my Friend

Detective Structure

Note that NPCs do not actually need to be able to perform actions that change the game state, and more specifically players do not have to able to interact with them at all. The core of NPCs are their role in a Narration Structure, and as such they can exist only as Diegetically Outstanding Features or only be seen through Cut Scenes.

Diegetic Aspects

One design goal with NPCs can be that they should be believable as humans or self-aware individuals with the same emotional and social responses as those associated with humans. This can be rephrased as the goal of making players take an intentional stance towards the NPCs when anticipating their actions. This may be an unreachable goal using current technology but temporary successes are possible (most famously shown already with the ELIZA program in the 1960s). The suggestions below provide options that designers can apply depending on how much effort they wish to put into placing people in an intentional stance and keeping them there.

A basic requirement for this to be possible is that the NPCs is in a Game World so that it has a space to act within (possible the real world for games using Real World Game Space). How they behave in this world needs to have Diegetic Consistency for the NPC to fit there, and this may require Awareness of Surroundings, Context Dependent Reaction, and Memory of Important Events. The NPCs in the Fallout series partially exhibit these characteristics: they make comments about their surroundings and commonly known world events but ignore corpses in their immediate proximity.

A second basic requirement is that they are Agents. As mentioned earlier, this is typically done through Algorithmic Agents or Game Masters but can in some cases also be done through Spectators. Examples of ways to increase players impression of NPCs agency (in contrast to simply making them more powerful) includes providing them with Initiative, Own Agendas, Competing for Attention, Barge-In, and Unpredictable Behavior. The four first of these are present in the interactive drama Façade while the last one may result from the system's inability to parse player input - this does not necessary need to be a bad thing and is part of the reason why ELIZA works (in combination with using Ambiguous Responses). Others fortune affects own Mood is related both to having Diegetic Consistency in response to what happens in the Game World and to having agency - it can be expressed through how Memory of Important Events are made visible or through attacking those that threaten others in one's Faction. For games striving for Replayability, it can be important to provide each NPC, or at least for the most important ones, with an Open Destiny to avoid risking that players take the NPCs experiences as predetermined and thereby not necessary to involve oneself in.

Another aspect of NPCs Diegetic Consistency is how player can interact with them. That one cannot interact in all the ways people can interact with each other in the real world is typically accepted just as one cannot perform all the actions possible in the real world. However, when there are inconsistencies in that one can perform certain actions towards some NPCs but not others problems can arise (the same goes when some NPCs can perform actions and others cannot but diegetically should be able to). For example, it is not possible to attack NPCs of your faction in World of Warcraft. Although this might be argued to be Enforced Agent Behavior to preserve the Diegetic Consistency it can also be seen as limiting players' Freedom of Choice and limiting the Creative Control of players by making the Roleplaying of their Player-Created Characters difficult or impossible. However, allowing this can ruin Narration Structures and lead to Unpredictable Consequences for other players. Another example of this is the inconsistency in the Fallout series regarding if it is possible to kill children or not. Besides the moral issues related to these types of design questions, typically trying to acknowledge these possible actions requires more resources in the development of game and may only be worthwhile if one if aiming to support Sandbox Gameplay.

There is actually another, even more basic, aspect of making NPCs to have Diegetic Consistency. This is that their representations should mimic their states as appropriate for the setting. In games like the Super Mario series this may be that the Bob-ombs Enemies flash and sound before exploding while in games with high granularity in their Combat system such as the Fallout series this may require Visual Body Damage and Dissectible Bodies.

Interface Aspects

The amount of interaction available with NPCs can easily become overwhelming. Although breaking Diegetic Consistency, this is often solved through the use of Secondary Interface Screens to provide separate interfaces (and modes of play) for activities such as Trading and Dialogues. The cost of this is making Barge-In more disruptive and Gameplay Integrated Conversations impossible.

Consequences

Since the creation of any NPC implies a Game World it consists in, have a NPC either requires a more fully developed Game World or creates one anyway but without Diegetic Consistency. Further, since the core of NPCs is to present a diegetic person it is at odds with the Units patterns, both because NPCs typically have some individual variation and that they by definition are not controlled by players.

While giving NPCs Preventing Goals introduces Conflict and possibly Combat in games, Cooperation and Team Combos can be achieved through giving them Supporting Goals instead. Agency of any type in connection to NPCs automatically provide Enforced Agent Behavior and typically leads to Complex Gameplay (except when used in conjunction with Supporting Goals when it instead can provide Casual Gameplay). This complexity is typically multiplied by the level of detail put into the Character connected to each NPC, if any.

Relations

Can Be Instantiated By

Game Elements

History

New pattern created in this wiki. However, most of the material is collected from earlier research papers .