Brenner

Brenner was a phaser specialist aboard the USS Enterprise, under the command of Captain James T. Kirk. He was on duty in the phaser control room during the Romulan incursion of 2266. (TOS: "Balance of Terror")

Although not referenced on screen, Paul Schneider's script for "Balance of Terror" names this character (along with Fields) as a phaser specialist. Brenner was played by Sean Morgan, who also portrayed Harper and O'Neil.