What is an NPC?Edit
An NPC is a "Non Player Character", meaning that all actions made by said character are controlled by the game itself and not another human. Most NPC's have programmed responses they give, show, or tell within a game's story line. Some games do, however, add in the "unknown" factor to make it appear more random in the actions done.
In any case, NPC's can add to the final outcome of the player's gaming experience. Some games put certain NPC's at "vital", or "climax" points of the game where your actions will affect how the game turns from that point. Also, as in Wonderland Online, some NPC's that have quests, also have different rewards depending on either your response, or your primary elemental skills.
In all games, NPC's add quite a bit to the depth of the game, and help to keep the player's interest fresh.