"Errand of Mercy" is an episode of the original science fiction television series Star Trek. It was originally broadcast on 23 March 1967. It is episode #26, production #27, written by Gene L. Coon and directed by John Newland. This episode marks the first appearance of an alien race known as the Klingons.At war with the Klingons, Captain Kirk and his First Officer, Mr. Spock, attempt to sway the incomprehensibly placid population of a planet to resist an invading military occupation.