A robot guardian appeared to be a robot constructed on planet in Sector Vega 6 to guard the Sceptre of the Sun.
In the year 2264, officers from the USS Enterprise acquired the Sceptre for Chang, but were prevented from leaving by the robot guardian. Captain James T. Kirk tried to use the Sceptre on the robot, but it had no effect. Instead, Spock had the party distract the robot while he climbed up a hillside, jumped onto the robot's back and ripped out a set of wires, disabling it. However, he was puzzled that a robot, a product of science, was guarding a magical sceptre, and after returning to Chang with the Sceptre, revealed that he had deduced that the robot was merely an illusion created by Chang. (TOS comic: "Sceptre of the Sun")