Morton was a UNIT soldier who served under Brigadier Lethbridge-Stewart.
He helped search Stanbridge House for Broton. When the Fourth Doctor found the Zygon, Broton killed Morton by strangling him. (TV: Terror of the Zygons)
Behind the scenes
Alan Clements, who played Morton, received no on-screen credit.
Another UNIT soldier named Morton appears briefly in Doctor Who and the Silurians. It is unclear whether they are meant to be the same character.