Non-player character
A non-player character (sometimes "non-playable character" or non-player class), shortened NPC, is a character in a role-playing game or computer game whose actions are not controlled by a human player.
Role-playing games
In a role-playing game, an NPC is controlled by the gamemaster. Non-player characters populate the fictional world of the game, and can fill any role not occupied by a player character (PC). Non-player characters might be allies, bystanders or competitors to the PCs.
NPCs vary greatly in importance—from the NPC innkeeper seen once by the player characters, to the NPC arch-nemesis that comes back time and again for an entire campaign. While every inhabitant of the game's world except the PCs are NPCs, very few are given any detail by the gamemaster (GM). In fact, most of the minor ones are invented on the spot as needed—doing this well is in fact one of the hallmarks of a good GM. There is some debate about how much work a gamemaster should put into an important NPC's statistics; some players prefer to have every NPC completely defined with stats, skills, and gear, while others define only what is immediately necessary and fill in the rest as the game proceeds. There is also some discussion as to just how important fully fleshed-out NPCs are in any given RPG, but it is general consensus that the more "real" an NPC feels, the more fun players will have interacting with him or her in character. Gamemasters should remember that just as a player character has hopes, dreams, and goals, so does every NPC, and ignoring such elements tends to lead to 'cardboard-cutout' personalities that are boring and/or over-simplified.
Playability
In some games and in some circumstances, a player who is without a player character of his or her own can temporarily take control of an NPC. Reasons for this vary, but often arise from the player not maintaining a PC within the group and playing the NPC for a session or from the player's PC being unable to act for some time (for example, because they are injured or in another location). Although these characters are still designed and normally controlled by the gamemaster, when a player is given the opportunity to temporarily control these non-player characters it gives them another perspective on the plot of the game. Some systems, such as Nobilis, encourage this in their rules.
Dependents
Many game systems have rules for characters sustaining positive allies in the form of NPC followers, hired hands, or other dependent stature to the PC. Characters may sometimes help in the design, recruitment, or development of NPCs.
In the Champions game (and related games using the Hero System), a character may have a DNPC, or "dependent non-player character". This is a character controlled by the GM, but for which the player character is responsible in some way, and who may be put in harm's way by the PC's choices.
Computer and video games
The term non-player character is also used in computer role-playing games to describe entities not under the direct control of players. Nearly always the connotation is that an NPC is allied with, or at least neutral toward, the player, rather than being an enemy.
NPC behavior in computer games is usually scripted and automatic, triggered by certain actions or dialogue with the player character(s). In certain multi-player games (Neverwinter Nights, for example), a player that acts as the GM can "possess" the player characters, making them react like a NPC in a pen-and-paper game. More complex games, such as the afore-mentioned Neverwinter Nights, allow the player to customize the NPCs' behavior by modifying their default scripts or creating entirely new ones.
The level of dialogue by NPCs depends on the game. In many the majority of NPCs have only a few bits of dialogue, only acting as "signposts". This was the case for most very early RPGs and some developers have continued this pattern in current games. In more advanced RPGs, dialogues with NPCs are usually very complex. (For example, in Ultima series of games, parts I–III followed the first pattern, but later games had branching dialogue trees for each NPC.)