NPCs, or Non-Player Characters are effectively every character in a game that is not played by one of the players at the table. These characters are almost always played by the GM. This term encompasses all enemies and generic civilians as well as major characters the players interact with. These characters can be minor to the point of having no name and major to the point that they become an additional party member played by the GM. Sometimes GMs use this to fill a vacant spot in a party so that they are not too weak to deal with future events. Sometimes this takes the form of the mentor character who trains and guides the players while they are at a low level before leaving or being killed at a later time.
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