Robot chessmen were robots created by the children of Argylus which resembled medieval knights.
In 2266, a landing party from the USS Enterprise arrived on the surface of Argylus, where they were confronted by the robot knights. Hikaru Sulu compared the situation to being in a chess game, thus naming their foes. When their phasers on stun setting proved ineffective, a higher setting destroyed one, revealing their true nature. However, they were outnumbered and the knights soon captured them, seized their phasers and communicators, and took them to King Simon. (TOS comic: "Child's Play")