William Smithers played R. M. Merik, the merchant captain who became First Citizen Merikus on a Roman-style planet, in the second-season episode Bread and Circuses.
William Smithers (born 1927) is an American actor later known for the series Dallas. In Bread and Circuses he plays Merik, commander of the survey vessel SS Beagle and a former Academy classmate of Kirk who was dropped from Starfleet training.
Six years after the Beagle was lost, Kirk finds him on planet 892-IV as Merikus, adviser to Proconsul Claudius Marcus. To save himself he had ordered his crew down to the surface, where most died in the arena.
Merik is ashamed before Kirk and treated with open contempt by Claudius. In the end he throws a stolen communicator to Kirk so that the landing party can be beamed out, and is stabbed by the proconsul for it.