During the final episode, Gi-hun meets Il-nam at a hospital and learns that he actually organized the games.
The reveal is one of the biggest twists of the season, but viewers who were paying close attention may have caught some of the hints leading up to this.
Player 001's file is not there when Jun-ho looks at the list of this year's contestants, which starts at player 002. Also, we never actually see Il-nam die — we just hear an off-screen gunshot.
The rioting in episode four is also only broken up by the staff members after Il-nam begs for it to stop, saying that he's scared and worried they'll all die. The Front Man actually listens to his plea and tells the guards to step in.