“You’ll tell me your name right now, whether you like it or not!”
But the knight didn’t make a sound. The boy was furious, and jumped down and said angrily: “You will tell me! You have no choice!”
He’d never seen a corpse before.First Continuation of Perceval
There’s reasons to call these things other than PC (“player character”) and NPC (“non-player character”).
Cortex Prime, for instance, uses PC and GMPC (“game moderator player character”) - emphasizing that these characters are still being run by the GM and the GM is still a kind of player.
In another direction, King Arthur Pendragon uses PK (“player knight”) and so on.
Characters here are not so universally knights, and I can’t unlearn “NPC”, though. So those names will stick.