Doctor M'Benga was a Starfleet medical officer who served aboard the USS Enterprise under Captain James T. Kirk during his original five-year mission. In the event of Chief Medical Officer Leonard McCoy's absence, M'Benga became the ranking CMO.
He conducted his medical internship on Vulcan, an experience that made him particularly skilled in treating members of that species. In 2268, M'Benga treated First Officer Spock for a serious gunshot wound. He had to slap Spock violently to bring him out of his Vulcan healing state. (TOS: "A Private Little War")
Later that year, Dr. M'Benga supervised his colleague, Dr. Sanchez, with the latter's autopsy of transporter operator, Ensign Wyatt, who had died after the Kalandan Losira merely touched him. M'Benga reported that Wyatt's entire body had suffered cellular disruption: the touch "blasted" every cell in his body from the inside out. In reply to Spock's inquiry regarding the incident, M'Benga explained his fellow clinician Sanchez found no known disease-causing organism was responsible. He later reported that Engineering Technician, John B. Watkins, had also died from a similar cellular disruption.