An NPC (non-player character) is a friendly 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, selling items to players in exchange for coins, and can be sold items by a player in order to obtain coins, though some NPCs perform other functions.
Most NPCs are "Town" NPCs, appearing after certain milestones are achieved in game advancement (details below). They move into structures the player builds, known as Houses, which are generally required for Town NPCs to remain available.
Town NPCs that have moved into Houses reduce enemy spawn rates in the area, an effect that multiplies the more of them are present. With four or more Town NPCs in close proximity, enemies generally stop spawning on or near the visible screen altogether. Players tend to utilize this effect by building large structures ("Towns" or "Bases") with several integrated Houses, to serve as their safe haven. Enemy spawn rates in the area return to normal, or are elevated, during Events such as a Blood Moon or Goblin Invasion.
Town NPCs generally walk around during the day, and remain still in their assigned Houses at night. They have finite health and can take damage from enemies or Lava, and can die, though they will respawn following a delay as long as a suitable vacant House is still available. NPCs cannot be attacked by players, and their health regenerates over time.
There are currently 20 Town NPCs. An additional 2 NPCs will be encountered that don't move into Houses.
Town NPCs require a suitable, vacant Home built by a player (commonly referred to by players as a House). A House is a confined room enclosed by a frame of blocks, with a Door, background Walls, and two furniture items. Certain types of furniture are required, as well as certain room dimensions (see Home for details). Houses must not be located near Corruption or Crimson, and if those spread too close to an occupied House, the NPC living there may move out.
The Guide and Old Man are unique in that they always spawn upon creating a world. The Guide will also move into the first House you build. If he dies, he will need a proper House to respawn. The Old Man does not move into a House, but always appears near the Dungeon's entrance, and respawns the following day if killed. He despawns permanently once Skeletron is defeated.
If a House occupied by an NPC is damaged in a way that makes it invalid, the NPC will move out and walk around the area until a suitable House is restored. If killed, the NPC will respawn again whenever a new House becomes available.
 Buying and selling
Items can be bought simply by right-clicking an NPC and taking items from their inventory while their cost in coins is available in the player's inventory. Holding the right mouse button will allow the player to buy an item in bulk, so long as the item is stackable. The buy speed increases the longer the right-click button is held. Certain NPC's will sell Biome Specific Items if their House is located within a specific biome.
All NPC vendors can also be used to sell your unwanted or surplus items to gain coins, simply by placing your unwanted item(s) in their inventory. Items are always sold to vendors at one-fifth their purchase price. Not all items have a sell value (very common items such as Dirt or Wood have no value). Hovering over your item while the NPC's inventory is open will show its sell value. 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 returning bought items, which must be sold back at their standard sell rate of one-fifth the purchase price.
All NPC vendors buy and sell at the same price.
 Non-Town NPCs
|The Traveling Merchant randomly spawns once you have at least 2 Town NPCs, and will stay for one day. He sells a random selection of unique items.|
|The Old Man is found at the entrance to the Dungeon. He summons Skeletron, but only at night. Once Skeletron is defeated, the Old Man is no longer present, as (it can be inferred) the curse he was afflicted with is removed and he becomes the Clothier.|
 Town NPCs
This list is in the order that most Town NPCs would generally appear.
 Normal mode
|The Guide spawns with the player when they start a new world. He provides tips and crafting recipes.|
|The Dye Trader sells the Dye Vat crafting station, which allows you to craft and mix Dyes. The Dye Trader is acquired when you have any item used to make a Dye, or Dye itself.|
|The Merchant is acquired when all players combined have more than 50 in their inventories (or 1 player). He sells certain basic tools.|
|The Demolitionist is acquired when you have an explosive in your Inventory. He sells explosives, and, in hardmode, Hellfire Arrows and Explosive Powder.|
|The Painter sells paints and equipment used to paint blocks and walls different colors. Acquired after having three other Town NPCs.|
|The Nurse is acquired when you have found and used a Crystal Heart to increase your life capacity above the initial 100. She can fully heal players in exchange for coins.|
|The Dryad is acquired when you have beaten a Boss other than King Slime and Wall of Flesh. She buys and sells certain nature/corruption items, and can tell the player the percentage of Corruption and Hallow in the world.|
|The Arms Dealer is acquired when you have bullets, or a gun that shoots bullets, in your inventory. He sells certain guns, bullets, and after the Eater of Worlds has been defeated, Unholy Arrows.|
|The Party Girl sells items that create colorful visual effects, such as the Bubble Machine, Confetti Gun, and fireworks. After acquiring 8 other Town NPCs, the Party Girl has a 2% chance of spawning at each dawn, after which she remains. If killed, she starts over with a 2% chance of spawning each dawn.|
|The Goblin Tinkerer is found bound somewhere underground after defeating a Goblin Invasion. He sells items such as the Tinkerer's Workshop, and can reforge tools and equipment.|
|The Witch Doctor sells the Blowgun, the Imbuing Station and various Fountains. The Witch Doctor is acquired after you defeat Queen Bee.|
|The Stylist can change your hair style, and sell a variety of hair products. You can find the Stylist in Spider Nests.|
|The Clothier is acquired after you defeat Skeletron. He sells certain Vanity items, including the Familiar clothes. Note: Once the Clothier arrives, the Old Man despawns permanently (they are the same person).|
|The Mechanic is found bound in the Dungeon. She sells wire and other mechanical items.|
|The Pirate can be obtained by defeating the Pirate Invasion, which occurs randomly (though rarely) in Hardmode. It can also be triggered with the Pirate Map, which drops from enemies in the Ocean biome. You can gain a Pirate NPC in any world, though the required item can only legitimately be obtained in Hardmode.|
|The Truffle sells the Hammush and Mushroom Spear after the defeat of at least one mechanical boss, and the Autohammer after Plantera is defeated. The Truffle is acquired when you have a house in a surface Mushroom Biome during Hardmode.|
|The Wizard is found bound in the Cavern layer after defeating the Wall of Flesh. He sells certain magical items.|
|The Steampunker Sells the Clentaminator, Teleporter, and other useful items. Obtained after defeating one Hardmode boss. This can be done in any world if the player uses a "Summon" item for a Hardmode Boss, even in a world that has not yet entered Hardmode.|
|The Cyborg sells the Proximity Mine Launcher, Rockets and Nanites. The Cyborg is acquired after you defeat Plantera.|
|Santa Claus can be acquired between December 15th and 31st after you defeat the Frost Legion. He sells the Santa costume and colored lights.|
- NPCs will take about 2 minutes to spawn after another NPC has spawned or dawn passes.
- Bound NPCs found underground can be freed by talking to them, after which they will always respawn whenever a vacant house is available. Having an empty room ready for them when you anticipate finding one will mean you will have convenient access to them from your Town earlier on, though this is not required, and building a house later will still cause them to spawn at that time.
- NPCs will not spawn during an active Event.
- Male NPCs will teleport to a King Statue when you activate it it, and similarly female NPCs will teleport to a Queen Statue when you activate it.
- 1.2: 8 New NPCs added: Steampunker, Truffle, Cyborg, Pirate, Witch Doctor, Party Girl, Dye Trader, Painter.
- 1.1.1: Bound NPCs now can be untied with Autopause enabled. Santa Claus added.
- NPCs now have random names given to them on World Creation. Their deaths will be reported with these names. Also other NPCs will use them in their quotes. Upon respawning after Death will be given a new random name.
- NPCs now may be told where to live using the new Housing Menu feature.
- Two NPCs of the same type can no longer spawn, even in a multiplayer world. (Previously that was two additional merchants and second nurse. They had multiplayer conditions.)
- 220.127.116.11: NPCs now look at the character.
- Shops now sell items back to you. Shift-clicking items will automatically sell them.
- New sound for initiating a conversation to an NPC.
- 1.0.4: Added an option that will pause the game while talking to an NPC in single player. It defaults to off.
- Pre-Release: Introduced.