Eli was a male Human civilian at the rehab colony on Tantalus V in the 23rd century. In 2266, he was a therapist. He had the same blank look as the other staff members and inmates of the colony; they had been victims of the neural neutralizer.
That same year, he operated the neural neutralizer at least part of the time, and conditioned inmates with it in the same manner Dr. Tristan Adams did. He detained Dr. Helen Noel from interfering when Dr. Adams used the device on Captain James T. Kirk. (TOS: "Dagger of the Mind")
Eli was portrayed by Eli Behar. In the end credits, he was credited as playing "Therapist".