S'Chn T'Gai Spock, more commonly known as Spock or Mr. Spock, is a fictional character in the Star Trek media franchise. Originally played by Leonard Nimoy, Spock first appeared in the original Star Trek series serving aboard the starship USS Enterprise as science officer and first officer and later as commanding officer of two iterations of the vessel. Spock's mixed human-Vulcan heritage serves as an important plot element in many of the character's appearances. Along with Captain James T. Kirk (William Shatner) and Dr. Leonard McCoy (DeForest Kelley), he is one of the three central characters in the original Star Trek series and its films.