For me, it was Prehistorik 1. An old DOS-based game where you controlled a caveman in a 2D environment, avoiding hazards, smacking dinosaurs with a club, collecting stuff and more. There's a 2nd part of Prehistorik, I think that's way better.
Prehistorik 1
Prehistorik 2
That's my first gaming experience I can recall... Or maybe Wolfeinstein 3D, I'm not sure.