NPC

A non-player character (NPC) is any character in a game, simulation, or virtual environment that is not controlled by a human player. NPCs populate worlds and can serve as information sources, quest givers, merchants, enemies, or allies. They help convey narrative, provide world-building, and create interactive systems for players to engage with.

Origin and development: NPCs have existed since early text-based and graphical games. They have evolved from simple, predefined responses to sophisticated AI driven by scripting, behavior trees, finite state machines, and more recently machine learning in some experimental titles. Many games use dialogue trees, inventory systems, and pathfinding to interact with players.

Types and roles: Dialogue NPCs carry stories and instructions; quest-giving NPCs assign tasks; merchants trade items; combat NPCs are adversaries or followers; ambient or crowd NPCs populate towns to create realism. Some NPCs are designed as companions with lasting relationships with the player character.

Technology and design: NPC behavior relies on AI components for perception, decision-making, and action selection. Pathfinding methods like A* and navigation meshes support movement, while dialogue systems manage conversations and stateful interactions. Scripting binds events, quests, and reactions to player choices.

Challenges: maintaining believability, avoiding repetitive behavior, balancing quest design, performance considerations for large populations, and ensuring NPCs respond consistently to player actions. Open-world games often use procedural generation to seed large populations.

In tabletop role-playing games, NPCs are characters controlled by the game master rather than by players, serving similar narrative purposes.