Benton first appeared in "The Invasion" as a corporal, initially as one of the Brig's key men and then as UNIT's radio operator. He then didn't appear again until "The Ambassadors of Death," halfway through Pertwee's first season. But then he appeared in virtually every UNIT story up until "The Android Invasion."
He moved up in rank rapidly during his tenure (perhaps UNIT has high turnover): Sergeant in "Ambassadors of Death," Warrant Officer in "Robot," and RSM in "Terror of the Zygons." He is last mentioned in "Mawdryn Undead," when the Brigadier says he is "selling used cars somewhere." This seems unlikely, somehow.
Benton was originally slated for a cameo in "The Five Doctors," but John Levene turned the appearance down because he thought it was written out-of-character.
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