An NPC, or non-player character, is any character or mobile within the game that is not operated by a player, in contrast to player character. Many NPCs are also former player characters, canonized in the game after successful storylines.
Most NPCs in the game will be automated parts of the world that can be interacted with in various ways. Sometimes an NPC will be run by staff for plot purposes. If a GM is actively piloting an NPC, they may appear on WHO with 'Npc' as their class.