An Enterprise lieutenant in the landing party that beams down to the ruined Federation outpost on Cestus III in 2267, where he is vaporised by Gorn weapons fire.
Lieutenant O'Herlihy appears in the first-season episode Arena. He is one of the tactical specialists, with Lang and Kelowitz, whom Kirk takes down to Cestus III in answer to what seems to be an invitation from Commodore Travers. They find the colony destroyed.
When Spock's tricorder picks up cold-blooded life nearby, Kirk sends O'Herlihy to scout. He has gone only a short way when he is hit by a disruptor blast and disintegrated, the first casualty of the ambush. Lang is killed soon afterwards.
Kirk drives the attackers off with a grenade launcher from the outpost's arsenal, and the pursuit of their ship leads to his duel with the Gorn captain. O'Herlihy was played by Jerry Ayres.