There's a huge number of characters in the show
The most obvious and important of these are geometric shapes: circle, triangle and rectangle. They are found everywhere: on business cards, guards' masks, and the scenery where the games take place. They are three of the four shapes that players can choose from in the game of "Cells", and make up the chalk drawing used in the final game of "Squid". When Gihoon, Sabeok and Sanwoo have a fancy dinner before the finals, the table is arranged in the shape of a triangle on a circular platform with a chequered pattern.
These figures have been interpreted as symbolic of human society. The Square represents the bulk of the population, the unconscious masses who simply go about their lives. The Triangle above it represents the privileged managerial class that commands them. The Circle below represents the poorest segments of society who are about to fall out and become prey to the games. The Upper Circle represents the shadowy top of the ruling elite who have conspired to create these games.