For the specific term “NPC” maybe, but the idea of “There is a main character and every one else is a machine” goes back much further - Kurt Vonnegut’s Breakfas

For the specific term “NPC” maybe, but the idea of “There is a main character and every one else is a machine” goes back much further - Kurt Vonnegut’s Breakfast of Champions (1973) tackles the idea in a particularly humorous way. (Not too much of a spoiler I hope, in classic Vonnegut fashion the bottom line is delivered up front and the rest book is about getting there) Note: don’t be tempted by the audiobook! The real deal features illustrations by the author