Ensign O'Herlihy was a male Human Starfleet officer in the 23rd century. He served in the operations division aboard the USS Enterprise in 2267 under the command of Captain James T. Kirk, during the historic five-year mission. He was one of the ship's ordnance officers.
That same year, O'Herlihy was one of three tactical aides who beamed to the Earth observation outpost on Cestus III in 2267. Arriving, they discovered the colony had been destroyed by the Gorn, a previously unknown species. Captain Kirk ordered O'Herlihy to stay with him. He was killed by disruptor fire, seconds after discovering the position of the attackers. Of the three aides, only Lieutenant Kelowitz survived this attack. (TOS: "Arena")