Thirty-Seven had a clunky appearance with a main rectangular core block, two jointed arms and two stubby legs. It stood about five feet tall with the number 37 written on it for identification. It interacted orally, using polite syntax, and through a large monitor screen using emojis.
Thirty-Seven was created by cyberneticist Robert Durant Williams in a facility five kilometers outside the Federation settlement On Calibus. Williams' experiments in cybernetics involved adding Human DNA into the brains of the robots in an attempt to make them more lifelike, but he had reached an impasse. Thirty-Seven was present when Britt mysteriously arrived to help Williams, with the result being new series of robots that spread a virus to all of the colonists. To keep Williams safe, Thirty-Seven and other robots secured him in the facility. It maintained the facility's power generator hoping for rescue.
Thirty-Seven was discovered by James T. Kirk, Spock and Leonard McCoy, who were fleeing from the infected colonists. Thirty-Seven brought them to Williams' lab, where McCoy studied data in the lab's computers to develop an antidote. Thirty-Seven warned them about Britt, so when she returned they were ready. After McCoy had stabilized the conditions of Williams, the colonists and their own infected security officers, Kirk thanked Thirty-Seven for its help. (TOS comic: "Infestation, Issue 2")