The puppet-like robots were less than three feet tall, did not speak, and were able to carry out instructions.
In the 23rd century, a number of Mortards were constructed by Doctor Rycho on the planet Raylo. They in turn built him a vast facility within underground caverns. Rycho considered the Mortards his slaves.
In 2266, a group of Mortards led a hypnotized James T. Kirk into a stasis chamber which was programmed to drain his life energy to power the robots. Other chambers held additional Humans, including Doctor Burton.
When Spock and Leonard McCoy searched the caverns, four Mortards captured them, leading them with some type of staff-shaped weapons toward Rycho. Mortards tried to drag Spock and McCoy into stasis chambers, but Spock struck one of them and it broke apart into dozens of pieces.