Non-player character

From Styleguide

non-player character

A character that is not controlled by a human. Usually used in role-playing games to refer to computer-controlled characters like merchants, innkeepers, townsfolk and others who aid in your quest. Do not use to refer to enemies.

NPC acceptable after first reference.

Example: Non-player characters populate Oblivion’stowns, saying captivating things like, "Sigh... times are tough" when you talk to them.

Wrong: non player character, nonplayer character.

Also see: artificial intelligence, bot, character, player.