An NPC is an automated Non Player Character. While NPCs technically include enemies/monsters, passive critters, and friendly characters, this wiki differentiates between the three classes of NPCs with the labels "enemy", "critter", and "NPC", and each have their own separate page on this wiki. This page is about the friendly automated characters who provide a service to players.
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. Some NPCs also perform other functions.
Most NPCs are "Town" NPCs, appearing after various milestones are achieved in game advancement (details below). They move into structures the player must generally build, known as Houses, which are generally required for Town NPCs to remain available. Each NPC will need its own house.

Town NPCs that have moved into Houses reduce enemy spawn rates in the area, an effect that increases 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. These reductions are usually overridden by Events like Blood Moons or Goblin Invasions, during which spawn rates return to normal, or are elevated, and enemies will once again attack players and NPCs in the area.

Town NPCs generally walk around during the day. They remain still in their assigned Houses at night. NPCs have limited health and can take damage, and ultimately die from enemies, Traps, Lava, or by drowning in Water; though they cannot be attacked directly by players (outside of special Voodoo Doll accessories or Rotten Eggs). Their health regenerates over time, and if killed, they will also respawn following a delay, as long as a suitable vacant House is still available.

Acquired When
Starting a new world.

Description
Provides tips,crafting recipes, and a general guide on how to get other NPCs.

Acquired When
All players combined have more than 50 in their inventories

Description
Sells basic tools and supplies.

Acquired When
A player has more than 100 health.

Description
Heals players and cancels debuffs in exchange for coins.

Acquired When
A player has an explosive in their inventory.

Description
Sells explosive items.

Acquired When
A player acquires a Dye item, or any item used to craft Dye, in addition to either defeating a pre-Hardmode boss or acquiring one Strange Plant Desktop
Description
Sells the Dye Vat crafting station, and provides reward dyes in exchange for rare plants.

Acquired When
A Boss is defeated other than King Slime, Lepus or Wall of Flesh.

Description
Sells nature/Corruption/Crimson items, and can report the percentage of Corruption/Crimson and Hallow in the world.

Acquired When
Eater of Worlds or Brain of Cthulhu is defeated, and he is found and spoken to.

Description
Sells items that summon and help fight the Old One's Army. Most cost Defender Medals, except for Eternia Crystals, the Eternia Crystal Stand, and Ale, which cost ordinary coins.

Acquired When
A player has bullets, or a gun that shoots bullets, in their inventory.

Description
Sells guns, bullets, and other ammunition.

Acquired When
Found and spoken to in a Spider Nest.

Description
Can change the player's hair style, and sells Hair Dyes.

Acquired When
After 7 other town NPCs are acquired including the guide.

Description
Sells paints, painting tools, and Paintings.

Acquired When
Found and spoken to in the Underground Desert.


Description
Sells Golf Clubs, Balls, and other golfing items.

Acquired When
Found and spoken to in an Ocean Biome.

Description
Gives Fishing quests and rewards players for completing them.

Acquired When
Found and spoken to in the cavern layer, after defeating a Goblin Invasion.

Description
Sells items such as the Tinkerer's Workshop, and can reforge items.

Acquired When
Queen Bee is defeated.

Description
Sells the Blowgun, the Imbuing Station, summoner equipment and Fountains.

Acquired When
Skeletron is defeated.

Description
Sells some Vanity items, including the Familiar clothes.

Acquired When
Found and spoken to in the Dungeon.

Description
Sells the Wrench, Wire, and other Mechanism-related items, in addition to the Mechanic's Rod under certain conditions.

Acquired When
Chance of spawning after acquiring 13 town NPCs. (or as few as eight in the console/mobile versions).

Description
Sells items that create colorful visual effects. If killed, she does not always respawn the following day as other NPCs do, rather starting over with a random chance of re-spawning each dawn.

Acquired When
Found and spoken to in the Cavern layer in Hardmode.

Description
Sells magical items.

Acquired When
A Tortured Soul is transformed with Purification Powder in the Underworld.

Description
Collects property taxes from other NPCs. Earns 50 Copper Coin per NPC present, collectible by the player.

Acquired When
A House is built in an above-ground Mushroom Biome during Hardmode.

Description
Sells the Autohammer, Mushroom Spear, and other mushroom-themed items.

Acquired When
A Pirate Invasion is defeated.

Description
Sells the Cannon and other Pirate-related items.

Acquired When
Plantera is defeated.

Description
Sells the Proximity Mine Launcher, Rockets and Nanites.

Acquired When
A mechanical boss has been defeated.

Description
Sells the Clentaminator, Teleporter, Jetpack, and other items.

Acquired When
The Frost Legion is defeated, appearing only from December 15-31.

Description
Sells the Santa costume, colored lights, Christmas trees and their decorations.

Acquired When
All other town NPCs are in the world (except for the Old Man, Traveling Merchant, Santa Claus, and town pets).
Description
Sells several vanity and furniture items.

Acquired When
22% spawn chance during morning hours (04:30-12:00 in-game time) once two other NPCs are present.

Description
Stays for one day, sells a random selection of unique items each day.

Acquired When
Starting a new world.

Description
Found at the entrance to the Dungeon. Summons Skeletron, but only at night. Once Skeletron is defeated, the Old Man moves into town as the Clothier.

Acquired When
Found randomly underground

Description
Sells Counterweights, Spelunker Glowsticks, Magic Lanterns, the Yoyo Glove and some other items based on the lunar cycle. Some items such as the Slap Hand can only be obtained from him.