Born into an old army family, young Lethbridge-Stewart showed such qualities of initiative and leadership that he was rapidly promoted to the rank of Colonel in Military Intelligence. During the Yeti invasion of the London Underground (The Web of Fear), he took charge of the investigative team, and when it was decided to set up the United Nations Intelligence Taskforce (UNIT) to deal with threats from other worlds, he was promoted to Brigadier and put in charge of the British operation.
He was a soldier through and through and his solution to every problem was a military one. After adventures with the third and fourth Doctors, the Brigadier had retired in 1977 and in 1983 met up with the fifth Doctor during his stint as a Maths teacher at Brendan College (Mawdryn Undead), later in that same year, he was kidnapped by Borusa in The Five Doctors and helped the second Doctor in the Death Zone, he later met the seventh Doctor in 1989 during the threat from Morgaine in Battlefield.
Nick's also reprised his role as the Brigadier in two audio dramas for
Big Finish and appeared with Colin Baker for the first time in
The Spectre of Lanyon Moor recently with Paul McGann in Minuet in Hell/Zagreus