Pitcairn (Lieutenant)
Lieutenant Pitcairn was a male Human Starfleet officer who lived during the mid-23rd century. He served in the operations division aboard the  under Captain James T. Kirk during the mid-2260s. 

In 2267, Pitcairn served as the Enterprises security chief when he accompanied Vinci to the bridge, in response to Spock's request for security to send up an armed team. Upon his arrival, he was informed by Doctor Leonard McCoy that Spock be put under arrest for mutiny and confined to his quarters.

Later, Pitcairn and another guard stood watch in the ship's hearing room during Spock's preliminary . After the hearing had concluded and Spock refused to return control of the Enterprise to Kirk, the captain ordered Pitcairn and his subordinate to lock Spock up, and they escorted him away. ()

During Spock's proceeding court martial the next day, Pitcairn stood guard outside and later inside the hearing room, as the Enterprise received a transmission from Talos IV. ()

Background information 
Pitcairn was played by actor Brett Dunham, who wasn't given an on-screen credit for the role.

 The name appeared in the "The Menagerie" script, where it was applied to the "Security Chief". 

In the script, at the end of the teaser for "The Menagerie, Part II", Pitcairn had a single line of dialogue which was unspoken on camera; this was to tell Spock, "Sorry, sir. We have orders to lock you up," before escorting Spock out of the hearing room along with another security officer. 

Furthermore, in the third act of the same script, Pitcairn entered the hearing room and announced, to a Talosian projection of Commodore Mendez, the arrival of Montgomery Scott and Leonard McCoy, who were there to report that they had found which computer Spock had tampered with. Although this scene was filmed, its deletion explains why Pitcairn makes an unseen transition from outside the room to inside the room. 
Humans
Starfleet operations personnel
USS Enterprise (NCC-1701) personnel
Deleted and unused material in background