Last Fall my roommate was taking a class on computer networks, he ended up inventing PID as a flow-control algorithm, though he didn't know to call it PID.
Oddly enough I too unknowingly implemented a PID controller without prior exposure to the theory. I was trying to make a stable hovering platform using only thrusters in Garry's Mod. I remember once I tweaked the parameters just right it was amazingly responsive and stable. I only realized what I had actually done years later.