NPC's are abbreviations for Non Player Characters. In Diablo II, they almost exclusively inhabit the towns of each Act, and offer various services to the player, including bying/selling items, repairing items, gambling, handing out quests as well as bantering about various topics with the player.
Technically, Mercenaries could also be termed as NPCs, however they are never referred to as such in the Diablo II community. They are instead called hirelings, or mercs for short.
There are several types of NPC's, and the five towns across the game: The Rogue Encampment, Lut Gholein, Kurast Docks, The Pandemonium Fortress and Harrogath all have the same basic types.
- All acts have one NPC that can repair items. These are the typical blacksmiths, and they also provide heavy equipment like armor, swords and axes etc.
- All acts have a healer. When talking to a healer, the players mana and hit points are fully restored, poison is cured and curses are removed free of charge and instantaneously.
- All acts have a NPC which you can gamble with.
- All acts have a NPC which can handle Mercenaries.
Deckard Cain is a special NPC. He is rescued when you complete The Search for Cain, and after that travels with you through all acts. He is key to completing several quests, and identifies all items in your inventory for free when you've rescued him. He always offers that service throughout the rest of the game after that.
Though most appear inside the town walls of the various acts, a few NPC's appear in the wilderness. They are:
- Blacksmith: Repairs broken equipment for the character in exchange for gold.
- Gambler: Allows the player to Gamble with a chance of winning rare items in exchange for gold.
- Healer: Heals the player and mercenaries for free.
- Mercenary Captain: Has mercenaries available for hire and resurrects dead mercenaries. (Note: Tyrael in Act 4 does not hire, only resurrect).
- Identify: Only done by Deckard Cain. He appears in every Act.
- Trader: Sells various items and equipment.
- Talk and Gossip: except few (Kaelan, Wilderness NPC's above), almost all NPC's also offer talk about various Quests and gossip.