An Arms Dealer is a non-player character (NPC) in Terraria who sells a variety of weapons and ammunition. He will move into a vacant house in any biome once certain criteria are met.
To get an Arms Dealer to move in, the player must have at least 50 silver coins and an empty house. The house must have at least one door, one chair, one table, and one light source. Once these criteria are met, the Arms Dealer will spawn in the house the next day.