NPCs

An NPC (non-playable character) is an automated character that provides some service to players. Players can utilize NPCs by standing near them and right-clicking on them.

Most NPCs are vendors, providing items in exchange for coins (and coins in exchange for items). Exceptions are the Guide, who provides information, and the Old Man, who is used to summon Skeletron. The Nurse, who doesn't sell items, provides Health restoration in exchange for coins instead. The Goblin Tinkerer sells items, but also provides the Reforge function.

Conditions
Most NPCs require a suitable, vacant Home built by the player. This is a confined room (completely enclosed by walls, wooden platforms or doors) with background walls, and certain furniture and space requirements. See Home for details.

Most NPCs also require that their specific conditions are met, usually meaning the player must achieve a certain level of advancement in the game. Examples include acquiring 50 silver coins for the Merchant to spawn, or beating your first Boss for the Dryad to appear. See the specific NPC requirements in the table below.

NPCs can be assigned to suitable homes using NPC Flags from the Housing Menu, where you can also check whether a room is a suitable home. Currently though, the Housing Menu checking tool is glitchy, reporting suitable homes even when some conditions are not met. Refer to Home for more extensive details.

The Guide and Old Man are unique in that they always spawn upon creating a world. The Guide will also move into the first home you build. If he dies, he will need a proper home to respawn. The Old Man does not move into built homes, but always appears near the Dungeon's entrance, and respawns the following day if killed. He despawns permanently once Skeletron is defeated.

It appears that NPCs will sometimes move out of their houses if there is Corruption nearby. NPCs will not move back in until the Corruption is cleared.

NPCs will take about 2 minutes to spawn after another NPC has spawned or dawn passes.

Selling
All NPC vendors can be used to sell your unwanted or surplus items to gain coins, simply by placing your unwanted item(s) in their inventory. Not all items have a sell value (very common items like Dirt or Wood, for example, have no value). Hovering over your item while the NPC's inventory is open will show its sell value. All NPC vendors offer the same amount of coins, at all times, for any given item.

Should you change your mind about a sale, sold items can be taken back in exchange for the amount you sold them for, as long you haven't yet closed the NPC's inventory screen. This does not hold true for items you purchase from an NPC's inventory, as purchases are permanent, and re-selling will not get you back the full amount you paid (sell value is always one fifth of its buy value).

Buying
Right-clicking an item will allow multiple purchases rather than purchasing it one by one.

Multiple NPCs
Note: This relates to a feature that was now deleted, although it has been confirmed that it will return on The Last Update by a developer's twitter account Source?

It is possible to have up to two additional Merchants in a multiplayer server, as well as another Nurse.

History

 * Santa Claus Introduced

(what are you still doing here? go and enjoy massive world of terraria)!