Lieutenant Bobby was a male Human Starfleet officer in the 23rd century. He served aboard the USS Enterprise from 2266 to 2267 under the command of Captain James T. Kirk, during the historic five-year mission. He served as a maintenance technician, security guard, and transporter chief.
While operating the transporter, Kirk addressed Bobby as a chief. (TOS: "Charlie X")
Bobby was frequently seen working as a repair technician, responding to battle damage and normal maintenance requests. (TOS: "The Man Trap", "Mudd's Women", "The Corbomite Maneuver")
He was also responsible for security detail in several instances and was attacked by Sulu when the latter was suffering from polywater intoxication. (TOS: "The Naked Time", "Tomorrow is Yesterday", "Operation -- Annihilate!")
Bobby also wore a sciences division jumpsuit, serving as a medical assistant at the bedside of Khan Noonien Singh. (TOS: "Space Seed")
Bobby was played by an unknown actor. The same actor can be seen in "Errand of Mercy" as a Klingon (guarding the door of Kor's office) and in a
Twilight Zone episode, "The Obsolete Man."
A post on Reddit.com stated that he was actually David Lee Ingram, (born 7 December 1941 in Los Angeles, CA and died on 25 July 2012) and was never credited because he never had a SAG card. 
's novelization of "Operation -- Annihilate!" referred to this character as Abrams.