Farrell was a personal guard of Captain James T. Kirk, aboard the ISS Enterprise.
During an ambush of James T. Kirk, Farrell saved the captain from an assassination attempt made by Pavel Chekov. (TOS: "Mirror, Mirror")
Farrell was played by actor Pete Kellett.
Farrell is a mirror universe character who apparently has no counterpart in the primary universe. He does not in any way resemble the first-season semi-regular bridge officer of the same name