The robot had artificial intelligence programming for medical procedures and autonomous activity. It was bipedal, covered with a reflective metal, and able to speak. It strictly obeyed commands from its programmed master, with polite deference to others.
In 2273, a medical droid was aboard the freighter Skorpius in order to assist in an illicit procedure. It encoded the the holostat patterns of Leonard McCoy into a forming pod so that its master, disgraced physician Anton Zauber, could assume the Starfleet officer's identity. It monitored the procedure while Zauber's wife Joann Zauber watched, politely turning down her requests to open the pod prematurely.
Afterward, it complied with the next part of the conspiracy. When McCoy boarded the freighter, Joann Zauber told him that nobody else was aboard, and the droid repeated the lie. After McCoy was dosed with a paralyzer drug, it obeyed Anton Zauber's orders to remove McCoy's clothes and lock him in an isolator unit. After McCoy and the Zaubers were transported aboard the USS Enterprise, it remained behind in the freighter. (TOS comic: "The Real McCoy")