The Non-Player Character Bank

A designed world, however beautiful, is still a script. Open-world games have mastered immersion through narrative, art, and music, yet their inhabitants remain bounded by authored conversations and relationship branches. Game players want more: randomness, free conversation and dynamic relationships. Large language models have begun to loosen the script, but between a model that talks and a character that lives, the distance is still wide. We present the Non-Player Character Bank (NPCBank), an ecosystem for crossing it. NPCBank Data grounds characters in source evidence and turns them into structured dialogue cases; NPCBank Web makes the resulting characters, evidence, and evaluation contracts open to inspection and annotation; and NPCBank Lab presents a demo game for testing interactions with model-based NPCs. NPCBank is based on a capability ontology, a contract-based case schema, and a construction agent that turns source material into character representations and dialogue cases. The first release contains 20,655 cases for 37 NPCs across seven games, covering 21 dialogue capabilities. Building on NPCBank, we formulate three challenges: supplied-state role-play, consumer-GPU inference, and long-horizon persistence. We find that models fail on different capabilities, consumer configurations expose distinct quality–memory and quality–latency trade-offs, and role-play remains fragile over long interactions. We release NPCBank as a foundation for building interactive characters across computational character modeling and game AI.