There are a few clues that point toward player one’s true identity as the organizer of the games.
Youngkyu Park
During the deadly first game of Red Light, Green Light Il-nam doesn’t seem fazed or concerned. Instead, he seems delighted to play. We later learn that he thinks playing the games is even more fun than making them.
He also seems to have a lot of knowledge about the games that will be played. He speaks about how familiar he is with marbles and his strategy helps his team win tug-of-war.
Il nam is also incredibly familiar with the neighborhood set for the marble game — likely because he helped create it.
In addition, after he loses the marble game, Il-nam is never shown getting killed. Viewers just hear a gunshot off-screen.
